gemrb, Comments from my most recent experience.
I recently, at most 2 months ago, compiled the trunk version of gemrb. I saw the impressive screenshots, and couldn't believe such an ambitious project could be so completed.
Unfortunately no recent install docs exist, and after going through about three installations, I failed to get a playable game. Projectiles would not equip, and other strange bugs, created an unplayable situation. Maybe gemrb will be a legitimate option, at some future point, but for now it's off the table.