GemRB is quite complete, especially regarding BG2, BG1 and IWD1 which can be played through. The whole Baldur's Gate saga is completable. There is of course still stuff to be done.
PST and IWD2 are not completable yet and require a lot more love to reach the level of the other games. Both can be played for several hours though.
There is also a work-in-progress demo in the repository, but it is currently not much more useful than the included minimal non-gui test demo.