Spider-Man: Edge of Time - I really wanted this one to be great after Shattered Dimensions, but it just misses the mark. The biggest problem is the complete lack of
Batman: Arkham City - Freakin' huge. I just completed the main storyline and only managed about 50% completion. A metric ton of stuff to do, which is always a plus. Kind of realistic looking damage to the costume and eventually yourself as you get shot at and beat up. Kind of wish there was a costume repair shop or something, but I guess when you're a superhero those are rare, especially when in an extended stay at a fortified enemy stronghold. I wasn't a big Batman comic reader so I can't say how well the characters were done, but from my understanding of all of the ones that show up (And a lot show up) they live up to my expectations. The voice acting is amazing, but that's to be expected when you've got Mark Hamill playing The Joker.
If given the choice, go with Batman. Definitely worth the price, especially if you played Arkham Asylum and have a basic understanding of the basic mechanics. Doubly so if you're a comic book fan, and you should just kill yourself if you haven't gotten it and are a Batman fan. The others are okay, but as like rentals.