Short version of my thoughts:
I FRAKIN' LOVE THIS GAME!!!!
I'm at about the 20% point, as far as getting through the game, and I'm not rushing. I am savoring the game, and already excited to go back and collect some of the Riddler's, well....riddles that I couldn't get to, or figure out the first time.
The mechanics of the game are top notch, the controls are fluid, and responsive. The camera work is well handled. I rarely feel like I can't see what's going on, or that one of the baddies got the drop on me because of the game. Because I mess up? Oh, hell yeah.
The graphics are excellent, and Batman looks as he ought too. A little too big, for my tastes, but I'm a guy who thinks most superheros ought to look like gymnasts, rather than weightlifters. The Joker is a little odd and plastic looking, but also very creepy and evocative. I'll roll with it.
The one area of gameplay where I can pick a few nits is in terms of figuring out how things work. Specifically, in regards to the Riddler's challenges, I only recently realized I missed solving a lot of them because it wasn't really made clear how to do so. (Essentially lining up day-glo question marks correctly in the "detective" mode.) I'm also curious about messages I see that say "every weapon has a special view, have you figured it out?" Puzzles, clues within the game? I'm A-OK with working those out, even the question mark thing is "fair," but game features really ought to be self-explanitory.
Where the game excels, beyond all my hopes is in the "feel." I feel like Batman when I play, and the game has mastered the multiple elements that make up Batman's skill set. Detective work, searching for clues? Check. Utterly brutal, dominating hand-to-hand combat? Check. Strategy? Laying in wait, planning stealth attacks from above and below? Check. Much like the recent Ghostbusters game, the victory here is in allowing the player to really feel immersed in the world presented. When Keven Conroy and Mark Hamill (from the AWESOME 90's Batman: The Animated Series) spar as Batman and The Joker, you feel like these are the real deal.
Good work. I want a sequel that leaves Arkham Island and goes into Gotham City proper...