I'll try to contain myself.
It seemed to go perfectly. In no particular order, the imagery was enticing, the story was gripping, the acting was brilliant, the directing was spot on. I've read plenty, seen plenty, and thought about plenty of post-apocalyptic scenarios and Washington's character makes every movement accurately. How he touches things, walks, talks, observes and measures and even what he takes, the character of Eli seems to be born for this situation. Everyone else seems to be born into their role, which is my only complaint.
You take a man and make him just power-hungry enough to kill and you have a villain. Make him someone you like and could even cheer for, and you have the perfect villain. I guess the screenwriter, Gary Whitta, skipped that second part. Every character - and they are all well directed and acted - plays their stereotypical role, even Eli. Not too much room for invention or character development, I suppose. The situation itself, "post-apocalypse," is becoming quite popular again and seems to the be complaint on everyone's lips.
After I see a movie I really love, I always look for negative reviews afterwards, to help me find balance. The primary complaints seem to be about the setting and the textbook characters. Also of concern to many is the religious tones of the book.
Book of Eli is based in the idea of faith. It is the main theme and it is going to be pounded into you, but pleasantly. It's gentle and it uses lube. The morning after, it will cook you breakfast and tell you that if you're uncomfortable doing this, that's fine, but you're welcome to come back. The ideas on faith are handled responsibly, as evidenced by the final shot of the film.
The twist is reasonable, exciting, and gives weight to the rest of the movie. Book of Eli was so well directed that I couldn't find any incongruent events after thinking on the film for an hour. It's just that well made.
I hope you enjoy it.