I have been following the updates on the beta and I would like to share my thoughts.
Terran:
After hearing discussion with a lot of Terrans, it would be better if the existing units we already have get a boost.
One thing which has been continuously discussed is the Siege Tank. Ever since the damage nerf on the tank, it has been underwhelming for a long time. Earlier in the game, maps were much smaller and may I say, not as well designed, and with the short distance from both players bases the tank was rightfully nerfed. But now, with the maps being larger and better designed, I feel like the old tank before Patch 8 ((version 0.10.0.14803) (except with 50 damage) can be tested again, and a lot of players would love to see this change that they have been waiting for a long time. I also feel the new ability in HOTS to pick up tanks when sieged as a Terran player, is highly overpowered and unfair to the other races.
Another thing greatly discussed over the years is the Ghost. A lot of Terrans feel that it's damage was greatly nerfed. A prominent feature that we had was the ability to go Ghost First in TvT, giving an advantage over the opponent just using marines, but was then completely ruined by the harsh ghost nerf. In my opinion a small buff could be given to the ghost and be trialed in order to open this sort of strategy again.
If this change comes to the siege tank, I feel that the cyclone is not a needed unit, and most people I have talked to have expressed negativity towards this unit, just because of the simple OP and easy design it has. Also I feel that the liberator is also not needed as Terran's already have the Raven's seeker missile to use. This sort of unit was great in BW (Valkyrie) because the Wraith was a poor Air vs Air unit, therefore the Valkyrie was needed in order to have proper anti-air.
One cool feature that could be added are more abilities to the Raven, specifically abilities LIKE Irradiate or defensive matrix, not exactly them, but maybe similar, such as what has been done with blinding cloud. Also, a new defensive structure would be a great idea, as the other races have automatic defense structures, and it would be a nice addition to the Terran, maybe something like a Anti-Ground battery, Flame Thrower, Laser, etc. (Obviously it would be more expensive)
Zerg:
As I am not a Zerg player, I can not really comment in a way which represents other Zerg players, but I will share my thoughts nonetheless.
The one thing that has always bothered me is the Corruptor. In BW, the zerg had a fun type of suicide unit in the scourge, with a powerful anti air in the Devourer, but the corruptor just feels like a stock standard hard anti-air counter unit with no special use. It doesn't have Vikings ability to stutter back or land, it doesn't have Phoenix's micro mechanic or the Void Ray's interesting design. Therefore I feel like a better designed Anti-Air unit for the Zerg would be something they would appreciate.
One more thing is the Lurker's attack sound. Compared to BW's great sound effect which scared the player and gave the audience excitement whenever the scary noise of spikes coming from underneath the ground, the HOTS sound of a quiet sliver is extremely underwhelming. This is common with a lot of the zerg units, who sound much less scarier then they did in BW.
Protoss:
Same with Zerg, I am not a protoss player, so will only share my thoughts.
Firstly, this has been greatly discussed, the carrier. The new Release Interceptors ability is wonderful and the ability to leash the interceptors. But one more thing the Carrier needs is the ability for all the interceptors to heal once they return to the carrier. As you know, DPS in Starcraft 2 is much higher compared to BW. Therefore I believe this ability is even more needed in the former then it was needed in the latter.
One thing also discussed by almost every protoss. Is that Gateways (not warpgates) have slightly quicker build times, for players who wish to use Gateways instead in a viable way. It would be a great feature for Protoss players to have the ability to choose one or the other. I know this might be potentially overpowering with Chrono Boost, but I am sure some sort of balance can be found.
On a more personal note, I feel the design of the colossus since it's inception is quite... Crappy ? Laser Wars is almost never fun to watch or play, but I actually don't know how to replace this sort of unit. Personally I think it should be removed, but I am not a protoss player and can't really comment.
Thanks for reading, please please please discuss.
P.S Protoss Mind Control ? :D