Also Note: All formatting was removed during the copy/paste, and since I already spent two hours on this, I'm not fixing it.

Alright, a few things before I explain my thoughts on how the D3 Beta feels and plays out.
Firstly - I am first and foremost a Starcraft II player, this will probably bias my opinion more than anything else, because I am used to a certain setup, and usually don't stray too far outside my little box.
Secondly - I have played every Blizzard game (Except Diablo I, but who's counting?
) and know exactly what I like and what I don't like about each and every one of them. I played Warcraft I, II, and III (Although these games will not be mentioned from here on out, I feel it's important to mention), as well as World of Warcraft. Diablo II was the largest part of my time two summers ago, when both me and my father played through the entire game to level 99 twice. I love Blizzard, I respect their work, and I mean them no disrespect in anything I may or may not say.Thirdly - I'm fifteen. "Oh my God, get out, no one wants you here, you don't know anything you stupid kid!" Yeah, I get it, I'm young and that will be another bias, but hell, kids play games too, right?
Now on to the Analysis
Okay, first, Diablo itself. The series has always been a very fun thing to play. Seriously, who doesn't love jumping into a world basically revolving around the Devil and his demon brethren to kill !@#$? Seriously? Tell me you don't feel empowered in Act I of LoD when you're near invincible and will never ever ever die. The hack and slash-esque genre is fun, even if you're only gonna play for an hour a week.
Diablo II was almost identical in every way concerning combat and map style. Dungeoneering is extremely similar, and the large hordes of mobs rampaging over a desolate landscape are still prevalent. It's awesome to feel an older game reworked, made much prettier, and dressed up to make anyone who plays it feel oh so good about killing that Wretched Mother who just won't stop spawning more mobs.
Now comes the bit that I'm dreading, the actual feedback. There aren't many things I'm not happy about, but those few things there are, hurt to hear. To me, anyways, I'm sure Blizzard has heard them a million times, and they may already have fixed them, but are keeping the fixes for release. Who knows? They could have made the game perfect by now....
Okie Dokie, let's start with something simple and easy. The environment. The feel of the game. Wow, how is it possible to make something look so good? I've said it before and I'll say it again, technology is amazing. Even being part of the Internet Era's children, growing up knowing how to build and program, knowing the internet inside and out, it's stupidly amazing what people can do with moving images. Think about it, the machine in front of you is taking electricity and making it into your desktop, these forums, this post, even the game I'm talking about!
Blizzard has used all of their new tools, the lighting, the sound, and the models, to make this as graphically pleasing as possible. Please note here that what we're seeing might not even be the highest quality, because we don't have many graphics settings. Think about that, that amazing thing that they have, they're making it better! Wow!
Not only is the game beautiful, but it sets the mood for every scene, when you're in town, it's dark, just like the cloud of despair and hopelessness hanging over it. Old Tristram, abandoned for years, lies broken and in shambles. A slight fog lies over the whole scene, as if the whole world's judgement and vision were clouded. The sounds are eerie where appropriate, such as a tomb, but the music, like the lighting, is always dark. The mood conveyed fits this world plagued by nothing but trouble and pain for years.
And now something harder. The gameplay. Although a very normal hack and slash, the sudden finds and intrusions into your sense of what is normal can be both interesting and annoying at times. For instance, the lore that you learn about in the game by killing different creatures can be annoying (This is, to my knowledge, a bug. On a Mac, at least [Yes, I'm on a Mac. Shut up, it's all my mother will buy], the pop up window with the subtitles to the audio will instantly appear, instead of appearing when you press the little "LORE" pop up in the bottom left, and you cannot shut it until you do click the aforementioned bottom left pop up. This means half your screen can be covered in a large fight and you have to listen to the audio to close the window that should never have opened anyways). The lore, when not in the way, however, is a lovely peek into the world of Diablo.
The storyline itself is clear after the beginning. It would be much nicer to have some backstory as to either the world, or at the very least, the fallen star. You can't really know that you saw something until your character mentions it, or you see it in Leoric's Cathedral. Other than that, it feels very clear as to what you are doing. I must admit, however, that it seems to move a little quickly. The fact that someone would instantly trust you to help kill their infected wife, or journey to their mother's hut to find her secrets, is slightly from left field. It affects the immersion a little too much, in my personal opinion.
The characters each play out in their own unique way, which is fantastic. I like the fact that each different character reflects a slightly, if not totally different play style. Being from Starcraft, this difference appeals to me, as it is akin to the different races in Sc2.
Okay, a brief break, I've been writing and contemplating this post for over half an hour. I need a drink....
Refreshing. Okay, back to gameplay. The actual fighting is... easy. This is by no means an issue, because it's not the complete game. This was exactly how Diablo II played out. Like I said, who didn't love destroying literally everything throughout the whole first act of LoD? I do hope, however, that the rest of the game progresses in difficulty as Diablo II did. The types of creatures are also part of this. The fallen were mindless, and the only thing you ever needed to worry about were a group of elite shamans who sat in a building and resurrected everything. That could be rough, if you weren't too skilled. However, fetishes in Act III were awful to deal with. They were small, so they could maximize all of your surface area to deal the most damage, and they were fast, bouncing in and out of range at every possible moment. The difference in gameplay and difficulty was one of the things that made Diablo II such a fun game, and helped to give it it's enormous replay value.
Dammit, here we go, the part I really don't want to talk about. The UI. Well, to say the least, the UI in this build is very give and take from Diablo II. I'm considering a compliment sandwich type thing here... but you know what, screw it, I'm no good at that. Ok, give and take, they gave us data. That's a large improvement over Diablo II. It's very much like the switch with Replay information from Starcraft: Brood War to Starcraft II: Wings of Liberty. The differences are astounding, in Starcraft I, you got the time and game speed. You couldn't rewind, and you could only switch to player views. That was it. In Starcraft II... well, go watch a cast, you'll see a lot of information in the top left corner, such as production and unit counts. In Diablo III, you see every stat of a weapon, instead of just attack speed and damage (Sure, durability too, but whatever), you get the Dps among other things. Have you ever been to the character sheet? Wow, it's stupid how much information you can get in there, and you can get more calculations and info from that!
Crap, my computer is lagging, probably from the length of this text, so let me post this and then write the rest in the second post.
Okay here's Post #2. Let's continue where we left off, shall we?
We went over the main part of the give, and now to the take. Blizzard, where's our customization? I hate so much to ask that. I really do. I feel like every other QQing, worthless, unnecessary poster on every Blizzard forum ever. But honestly, it feels, again, like the Starcraft replay system. In Brood War, you could watch Replays with friends, and now... well, now it's a source of great debate and frustration. In D2, we had the ability to go down a long and intricate tech tree of skills for each and every class. You could also customize stats in D2. This allowed people to play even each individual class differently than anyone else. That was something I always thought was fantastic. Although it may have taken you a few times through the game to get it right, you could play what you wanted to play how you wanted to play it. You could be a Necromancer with a horde of undead to do your bidding, or you could pair up with a single golem and use your superior damage dealing skills to get yourself through the boss, or the dungeon.
Blizzard has clearly stated that they don't want Diablo III to become an eSport, but why can't it be more competitive? For people who do want to play the game for the (perhaps) minimal PvP, why can't they have the ability to customize everything they need to be able to optimize their character?
Yes, I get it, the casual players would be overwhelmed! Not only that, but that would take an immense amount of design and careful planning to get right. The large amount of arrows in the characters' figurative quiver would have to be completely reworked and ordered very carefully. But after that's done, the casual players wouldn't have to be overwhelmed, after all, the framework for an automatic skill system and auto stat upgrades is already in place, why not allow an option for that to be chosen instead of choosing your own skills of stats?
Again, I know this is the Beta, and not all things are available, so this may already be in place, but if it isn't, I want my opinion out there for Blizzard to know there are some people who care.
Oh, yes, I forgot, the whole crafting system is amazing. I find it slightly too easy to gain the ridiculously good items this system grants, but other than that its well thought out and very useful. It's very different from WoW where the crafted equipment is useless for almost everything.
The Real Money Auction House is not something I'm going to go in to, I'm not sure anyone, even Blizzard, knows how it's going to turn out, and I suppose we'll have to wait and see. That and it's really controversial and I don't want to endanger this thread's hopeful neutrality if I can help it.
All in all, it's a great game, Blizzard, and I look forward to playing the full version. I hope this was helpful in some way or another, and feel free to debate anything I've said. I'd love to get your opinions.