First things first - this game is in BETA.
That means it is not finished, and therefore an objective review is not possible.
If you're going to base your opinions of a game on reviews of unfinished material then you'd might as well go home now.
On to business, I'm writing this to provide a more objective review than the wave of negativity.
The state of the game at time of writing is one in which the basic functionality works, but not everything is implemented. If you'd like to try this game do so with the knowledge that features may be missing or not working yet.
Overall impressions are good - the game feels identical to the previous installment and yet brings with it new mechanics and features which greatly improve upon it.
I was skeptical at first as a big fan of the previous game, and the genre in general.
In the early days I would tend to agree with some of these negative reviews, lots of bugs, lots of crashing, lots of lagging - but what do you know, they went and fixed all that (an example of why you should ignore reviews this early on!).
Colonies are much easier to manage than they were in the previous game, you simply choose you buildings up front and as you research new techs everything is upgraded for you.
There's a nice little feature where colonies can share space ports, allowing you to have (in theory) double the amount of production in that centre. This is great for players who focus on money, influence or other factors.
Starbases aren't finished yet so there is no point in reviewing them. Same basic mechanics as the last one with the addition of new modules and mining mechanics.
Combat is greatly improved, no longer do all of your weapons fire immediately and your mass of lasers simply destroys everything up front.
Now weapons have more realistic and varied fire rates, which can be modified by ship modules and research to customise your ships more (for example, loading lots of rapid fire mods onto powerful missiles).
Defence needs a bit of work IMO as defence are quickly worn down by weapons. Two shots from a laser with 30 damage will take out a ship with 60 shields. Sounds sensible, but there's nothing to stop you loading dozens of fighters with huge lasers to wipe out capital ships. Most Space RTS suffer from the same issue, so this is more a personnal bug bear than a problem.
Diplomacy is relatively straight forward, what you see is what you get. Tech, finance and treaty trading. The UN resolutions add some more dynamics but they soon get old when you realise 90% of them would hinder you...
Influence has been improved a lot, now if you occupy a planet deep within another player's influence it will be almost immediately transfered to the other player. This stops those pesky AIs colonising Mars for no discernable reason!
The tech tree is great in this game as you can either research improvements or new techs. "Do I really want a new type of laser, or do I want to improve the one I've got?". Obviously the answer to this will be "Eh, I'll take both thanks" but it's a good start and does much more to change the way you play "One more tech then I'll make my new ships, promise!".
Ship design has gotten a whole lot easier as internal hardpoints are now hidden, so it's much easier to attach things where you want them than it was before. Great for creative types.
Nothing on planetary invasion yet, so I can't comment here.
To sum up it's a good start and definitely work keeping an eye on it. Unless you're really interested in it's developmet there isn't much point buying it just yet (unless you're keen to get bonus stuff when it comes out like they usually do...).
Plenty of +/-ve reviews out there, none are helpful in the slightest at the moment. Keep watching, keep reading and reserve your judgement until you play it yourself or the full game comes out.
Hope this helps clarify what's what objectively at this stage.
Oh, the dev team has also been very good in responding to bugs and issues. I've seen bugs posted fixed within days (may be coincidence, but still!). Kudos - can't wait to play it.