Oh man, I finished Cloud Atlas, and it was amazing. I loved it. The structure - six stories forward into the future, 123456, and then finishing those stories in reverse, 654321 - could've been annoying, but it wasn't. I liked that it was different. I liked the way all the stories connected. The middle story, Sloosha's Crossin', had me intimidated before I reached it, as it takes place in the distant future and is written in a strange dialect. But once I got through three or four pages of it, it was no trouble at all.
The way Mitchell jumps genres is amazing. I got completely soaked up by the spy novel, or sci-fi interview, or whatever, far quicker than I thought I would. Somehow each story seemed completely unique and genuine, not like a quirky exercise Mitchell was attempting.
Should you read it? The only caveat I have is that not every story ends with a rosy happy ending. But it's not a downer, either. If you're okay with that, then yes, by all means, read this book! This is going to be a book that I push on people to borrow.