1. Buggy: I never had any stability issues, game is stable and the interface is very good Imo. It actually has a very low amount of annoyances, and im usually quite discriminating on this aspect. So I do not know what kind of "buggy" that meant but to me the game is stable and polished.
2. Game aspects broken by Twillight expansion: There will always be haters but in the facts this expansion has won much more awards and praises than complaints.
The only arguably "broken" aspects I can see is the fact that all the races have unique tech trees/buildings. But it's also the main selling point of the expansion. One could complain that it creates some imbalance issues and that some civs are OP and other weak etc.. Its actually true. But If someone complains that this ruins him/her gameplay ill just tell them to go Troll elsewhere, iirc you can actually disable this feature. Considering the game is a single player game, this imbalance is pretty much irrelevant if you ask me, in a multiplayer settings that would be different though...
Sure you can make your own tweaked custom civ that is optimized to totally Owns and go crush your opponent, if you hate that, then just dont do it!! Instead go make a weird crappy civ design with the objective of adding challenge instead. In the type of game that is Galciv2, this "imbalance" is in fact a blessing. It greatly increases the replay value and forces you to play differently with each civ in order to maximize the unique attributes. My goal when playing these types of games is to challenge myself and Galciv2 does it really well.
GC2 Ultimate ed is, considering how dirt cheap it is, actually one of the best bang for your buck i've ever seen in the history of gaming.
Furthermore, they added new soundtracks in the Twillight expansion and they are very good.