The expansion pack is almost perfect. It does what it says on the box; nothing less, nothing more. Stability is good, some occasional glitches, but nothing too important.
My only concern is cost. It costs almost exactly the same as the original game. I am not playing CIV4 scenarios and the benefits of this expansion pack is limited. OK, great generals is nice, new wonders are good (but there are only 3 of them in Warlords), new building types - finally here. The overall gameplay is still more or less the same.
If you are CIV4 fanatic, buy it, otherwise wait for few months and do not pay more than £10 for this. It is really good, but just not worth the current price.