My goal in creating this thread is to open up the subject of creativity within competitive melee maps. I am going to attempt to address some of the many of the aspects that go into making a map and how it relates to being creative. In the end, I hope this can partly explain why a lot of maps feel the same and how to change that on your own.
Conceptual Creativity is one of two categories that determine the creativity of a map. It is being innovative or unique through one or more of these categories: expansion layout, army positioning, base vulnerabilities, and game-play focus. In order to best understand each of these ideas, we must look at examples.
The biggest factor is expansion layout. This simply means how the bases are laid out and what order you take them in. Let's take a look a look at what is considered balanced in today's expansion layout.
The standard main and natural
This crude drawing shows the normal and balanced expansion layout for the main and natural. Ramps and flat ground chokes can be changed, but the same progression and number of entrances (one per main and one per natural) usually stays the same. For reference on current tournament maps that use this style, see Daybreak, Testbug, XelNaga Fortress, Shakuras Plateau, and TalDarim Altar. Once you have this basic design, you are only left three options for where you want to place your third.
Three options for a third
Option 1: Expansion against the main. This expansion is usually one or two levels lower than the main.
Option 2: Expansion outside of the natural, usually with its back to a cliff. This is normally at the same level as the natural.
Option 3: Expansion against the natural. Highground or lowground may vary.
These are realistically the only options because the game is balanced around having a close third. Without using one of these styles, your map becomes quickly in favor of certain races in different match ups. For reference on maps using Option 1 and 3 see Bel'Shir Beach, Testbug, XelNaga Fortress, and Shakuras Plateau. For reference on maps using option 2 see Starlight Breaker. For reference on maps using Option 1, 2, and 3 see Daybreak and Antiga Prime.
Since there are so basic few expansion layout options when using a single entrance main and natural, you are mostly limited to only being creative in the middle of the map. Do some searching on your own and take a look at the popular Brood War maps to see how they use creativity in the center when they choose the standard main and natural layouts (Most Competition BW Maps). For reference on creative SC2 maps using the standard layout, see Bardiche, Taonas, and Sanshorn Mist AE.
In order to work outside of these basic restrictions, the main and natural have to be altered. For reference, see many popular Brood War maps like Blue Storm, Destination, Chupung-Ryeong, Heartbreak Ridge, Adrenaline Rush, and Harmony.
Another main part of Conceptual Creativity is the game-play focus. This is a very difficult topic to explain. To me, it is how you want your map to play out; what play-style do you encourage, what army movement do you discourage, and what makes the map function differently than others. A great example is the Brood War map Katrina:
(2005) Katrina from Brood War
This map does an excellent job of having a very unique concept. The goal was primarily to encourage air play. To accomplish this, they have clearly put much thought and modification into the design of the entire map.
A) The main and natural discourage ground-based play. The natural is completely safe from any ground attacks. Since there is only one entrance, the defender has a very easy time holding off aggression from ground armies.
B) The expansions are spread out. Each expansion including the main and natural is distanced farther than on standard maps to increase the air vulnerability.
C) A lot of small chokes make moving a large army difficult. Without any open space except in the center, an army can get caught off guard very easily. Additionally, it means that expansions can be defended easier than normal.
(2008) Othello from Brood War
Othello's concept was to encourage harassment. This is one reason the map became such a popular map- harassment is hard to pull off and raises the skill cap in games. The player who plays better could do a lot of damage if their opponent isn't paying attention.
A) There is a cliff behind the natural. This is a very popular spot for drops and harassment throughout the game. A tiny opening allows the smallest units (zerglings, marines, zealots, etc.) to fit through to defend the drop.
B) The central third has a cliff behind it. Again, this is used for drops throughout the game.
C) The mineral only has two harass options. It is cliffed by the main, which means that a drop can harass the main and it at almost the same time. Additionally, the mineral only has a small area beside it that can be used for proxies or more drop harass.
In order to make a great map concept, you have to determine what your game-play focus is and then make modifications to capitalize on it. More examples may be added later. Note: It is important to understand that a standard layout can be just as fun and balanced as a non-standard layout. See Fighting Spirit and Python from Brood War.
The second factor that contributes to a map's creativity is the gimmick creativity. I only use "Gimmick" for lack of a better word. This category includes cliffs, chokes, gold expansions, rocks/mineral blocks, Xel'Naga Watch Towers, LoS blockers, occasionally backdoors/frontdoors, and aesthetics. Adding some of these aspects in can give some flavor to any map. But keep in mind they do not compensate for non-creative expansion layouts.
Gold base offers a sneaky third
A great example is the gold expansion risk vs. reward. By placing a gold expansion on your map, it often gives incentive for players to skip the close expansion and go for the high income base even if it is more risky. Many of the current maps use this form of gimmick creativity to add more dimension to the gameplay.
Aesthetics capture the community
In the original version of Belshir Beach, its beautiful aesthetics grabbed the attention of the sc2 community. People raved about using it in tournaments despite the imbalances that existed at the natural (now fixed).
Two tiny central chokes
The two very small chokes placed outside of the natural on Sungsu Crossing AE provide a new feature in competitive maps. Despite the expansion layout not being new, the middle offers some entertainment somewhat similar to the Brood War maps Blue Storm and Loki.
How to Improve Your Mapmaking
Creating a very conceptually creative and balanced map is very difficult without a lot of professional testing. Don't forget that all of the popular Brood War maps that are conceptually creative had huge amounts of testing for balance. Starcraft 2 balance still isn't complete, and thus map balance is not complete either; we can't know exactly what makes a map balanced, but we can get pretty close.
Learn mapmaking slowly without trying to rush parts that you don't fully understand. Don't worry about being creative until you have made some experience in standard maps- otherwise it won't work. The best way is to work some simple maps to start with, then begin to delve into the concept and creativity afterwards.
Once you have the basic knowledge, try developing concepts for your maps. Really put the time and thought into how you want your map to play - why style is encouraged, etc. When you have your concept idea, adjust your map accordingly instead of only changing for balance reasons.
* I hope to update this post as I find more information to add.