I decided to chance the full version after enjoying the demo (I haven't played a large scale space empire building game in a while).
I have a couple pet peeves with it:
The ridiculously low unit count- You can build as many units as you want, but you can only "warp in" or "shuttle in" 20 units at any given time. Once you lose units, you can hyperspace in replacements until your fleet is destroyed. It's not quite as noticable in the initial space battles, but in late game fleet battles or when skirmishing it really shows- especially if you're playing with a friend against multiple computer enemies- it's really frustrating that you can't muster the units to both maintain an offensive and guard your rear areas. Granted, C&C Generals has spoiled me on unit counts, but even Starcraft's 200 wasn't so bad- but 7 units for land skirmish battles? That's downright ridiculous.
The inability to warp out individual units- The unit count is also a pain if you have a cruiser or frigate with almost all its hardpoints blown off- you can't make that one unit hyper out so a "fresh" unit can hyper in. At certain critical junctures, this can drive you insane, for instance, if you have a frigate with no turrets left, and your starbase is under attack- even though you have other frigates that can warp in when the disabled one finally bites it (per the unit count).
The AI is weak- I've only really played skirmishes, the campaigns and a short galactic conquest game, but the AI never attacks your rear areas on the galactic map. Occassionally during space battles you can sit back and blow apart someone's space station from a distance using missile cruisers- and even though you are dismantling the starbase, the fleet around the starbase often won't rush the missile cruisers. Another noticable problem is that the AI doesn't go maurading from world to world with its space fleet- It'll pick one planet, invade, and just sit there if it loses the land battle. If you have a strong land army on that planet (such that you can fend off most ground assaults)- you've effectively immobilized their fleet until you can muster a counterfleet.
The Empire's lack of ground air units- both side gets a carpetbombing superweapon, but only the Rebels get a genuine air unit. Given that only one unit type and one type of turret can shoot back at air units, it makes the land part of the game feel a little unbalanced, since the unit counts are so low (if a Rebel player builds air units, the Imp player has to devote at least 1/7 of his army to anti air units- units that are worthless against any other type of unit).
Final prognosis- I wouldn't buy it. It's fun for a couple hours until you realize the limitations of the game, and then it very quickly becomes tedious. If you do want it, wait a couple months for the price to drop.