Welcome to space opera.
Gameplay is very similar to predecessor, it have same simple system but there are few injections and RPG elements in between missions. After each mission you find yourself at your mothership where you can access laboratory, armory, bar and bridge. Most missions reward you with research points(there are 2 types, used in lab) and money(used in armory), both used for upgrades. You also chat with crew, watch news on TV etc. This is actually very similar to Bioware games like Mass Effect 2 with maybe only exceptions that you don't have choice in conversations - just click on character and watch animation and that you navigate in ship by clicking on menu. There is no character alignment or such, but there are few choices during game where you can even loose companion. Developers decided to divide game into 3 episodes similar to latest Half-Life series, so you play only for humans this time with exception of about 4 missions whose you play for Protoss as sidequest. Overall game have about 25 missions(my case) in single player campaign. Gameplay itself during missions is just what you would expect, but I really like how each mission give you some twist or different objective/conditions to complete. It does feel much more variable and entertaining than other typical strategy games.
In general, game is very fine and there is nothing wrong, its pretty stable and bug-free as well, however I have to say few things:
First of all, you cannot zoom-out enough. I don't expect Supreme Commander here but still this limit feel old. Also, depending on your monitor aspect ratio, you may not see much on screen if you have 4:3 or 16:10. You will see most on 16:9 and it doesn't matter what resolution(or so it seems). Google it to learn more. I have 20" NEC S-IPS which is 4:3, my bad. 4:3 is worst for this game, but it didn't bothered me too much. This may also be unfair if you play online.
Second, I said between missions you interact with the crew almost similar to Bioware games. And just like their latest games, here too some dialogues and voices feel flat and boring. Game have very professional dabbing and all, but characters may feel "slow" sometimes and their tones may make you feel strange. Often a lot of uninteresting content or just to tell story, but there are also many great unique sequences. Its definitely not as bad as it sounds and definitely not as bad as some Bioware games(DragonAge ough......), but for so-long-in-development game and of this caliber I expected more. If you wonder "WTF you want?!?" then look at content of cutscenes and dabbing from Rockstar games like GTAIII:VC,SA,IV. Thats what I call "conversations" full of life, energy, natural feel, personality and things that makes you remember them. I still remember today epic cutscenes from W3:FrozenThrone, although those were animations 'cause at that time they haven't used 3D engine for character interaction. Maybe it was better that way. Here, most animations are unexciting TV news. I also felt for such number of missions and only one race there should be more twists and story content. Not even sudden attack on mothership. It was too straightforward although few decisions game left on you to choose did help.
Gameplay is very fine, but for only one race you play and number of missions, there should be more units, upgrades and more strategy. Also bigger maps, at least in the end. Supreme Commander gave me so many things to upgrade, several tech levels - units, protection fields, anti-nuke and much, much more.
Music is mixed bag. There are definitely great tunes especially in the end of game, but few others ruin atmosphere IMO. Blizzard try to paint main protagonist as a kind of "wild-west-cowboy" or "sherif", with tunes you would expect from such movies, but this is supposed to be space epic and therefore it doesn't fit to my taste - I rather what japanese sci-fi games play(Xenosaga series anyone?).
Graphics are ok and game can run on older computer just fine, but terrain and its shading is too simple. Buildings of your Terran race are just boxes without much inspiration. Even old C&C had more "tech" look to them. And this took them ages to develop, lol. Units however are truly superb. Cool mechs, large-scale ships and more.
First part of game may feel boring, also because new units and upgrades come s-l-o-w-l-y.
Physics and explosions are not that great. Forget smoke effects like in World in Conflict.
No in-game anti-aliasing option?!
So, thats about it. This is still after long time very decent old-school RTS and I look forward to next episodes to reveal more story of this space opera. In another 10+ years I guess.......