The good - atmospheric, tense, gripping, good performances, 3 or 4 brilliant shock scenes (as others have said, the girl crawling amidst lots of dead versions of herself was fantastic).
The bad - it just didn't really make sense, did it? My conclusion is that either I'm a bit stupid or the story doesn't quite add up.
Think my major gripe is the 'second' Jess managing to alter things so the couple doesn't die of shotgun blasts in the theatre. If all three Jesses are operating for each boat load of the group that turns up (and that is the case, isn't it?), then there's always a Jess that's in the each phase for every boat load ... so how can the couple sometimes die in the theatre and sometimes in the room and deck to satisfy each of the jess' experiences? Yeah? Also, she did keep her promise to death, didn't she? ... she always comes back ... or is that the point? Am I making sense? Is the film?
Anyway, the good outweighed the bad.