Maybe it strayed too far from the source material for him? It he went into the film without knowing anything about it an it wasn't his thing.Walked out? What the hell did he think he was going to get? There's been a talking Racoon, riding a talking tree in every trailer! What a tool. Some people want to be disappointed I think. It's cool if you genuinely don't like something. I understand that, but some fanboys have a habit of being over critical little pricks.
It was very close to the source material. I've read almost every Marvel cosmic comic since Annihilation, which is where this iteration of Guardians came from.
To your second point, if anyone can walk into a theater these days, not knowing a thing about the big summer movie with the millions of dollars of advertising behind it, my hat is off to them. Seriously, that individual has perfected personal media black outs. Good for him.