You mentioned that Crystalspace, Unity etc. are generic engines, but if you look at the forums you'll probably find everything you need, somebody already probably coded it. UDK is now in v2 and it has a cool scripting alternative, but, at least to me, the pipline is kind of complicated (and on that note Reality factory has a really messed up pipeline) and also, 90% games look very samey (Arkham Asylum, UT etc.).
You can try YoYo Gamemaker if you want almost no coding whatsoever, also has stuff already made to make a point and click game.
And on a bit off topic note: why the hate on Grim fandango, it's a game from 97 and it looks nice, it has better graphics than new S&M games.