Preface: I love the basic mechanics of this game and the Stardock way of business. That said, the game has some pretty glaring faults that have led me to take long breaks between playing. These are the two most obvious to me:
1. Scaling. As an empire gets larger, it should become harder to control, less efficient, people unhappier, etc... I mean this in the sense of both realism and playability. I won't go into realism since this should be readily apparent. In playability terms, it is what makes keeps a game interesting after you become the largest civ/race/whatever. Difficulties maintaining a huge empire while others recognize the threat and team up against it should be the norm.
I do not see this happen in GC2. Instead, there is no real penalty for overexpansion and no real threat to the largest empire. It's a case of the rich get richer. When this happens to me as the player, I lose interest once it becomes obvious I can easily win. Running the empire goes from exciting to tedious, so I rarely finish games.
2. Surrender. Others have argued over the surrender system. I'm with those who consider it silly and frustrating. An evil-leaning race should not surrender to a good-leaning race whom they've had little or no contact with because they lost a few irrelevant battles. (On a corollary, a race shouldn't pop-up the "The war...goes badly for us. Can you help?" diplomacy screen the very next turn after the war starts just because their military is weaker.)
Combine this with #1 and it makes the situation worse. Let's say the game is on a difficulty setting that gives the human player a slight disadvantage to the AI. The Torians are by far the largest empire, and the Arceans are winning a war against the Yor but have not taken a planet yet because we're so early in the game the battles are still between weak fighters and there are no troop transports yet. Suddenly the Yor alert the player that they have decided to surrender to the Torians "because they made the best offer." Not only is this a WTF?! moment but now the player has to decide whether the game is even worth continuing, as the most powerful race just went out of reach.
Again, allow me to stress that I really like the basic game engine. It just seems to me that more attention is given to the style (i.e. ship-building) than to the substance (i.e. playability). I suppose I am making these comments to see if others agree and, if so, perhaps they will be considered by the Devs in a future release. Or perhaps my experience has been different from others and I should keep plugging away.