I just got back from watching it. I knew almost nothing of these characters going in, and enjoyed it. I think it makes it more enjoyable not knowing some of the "secrets" about the characters ahead of time.
Seemed very different than the previous Marvel Universe movies, I could see that throwing people off. A group of younger watchers in the audience were not too happy about the movie afterward, walking out they commented that it was OK, but were hoping that it wouldn't continue this way.
Post-credit scene was just a big "WTF?" moment, still not entirely sure how it fit or why it was what it was, I'll look it up sometime soon. The pre-credit scene was cute though.
I did find out why my theater didn't have a showing closer to noon. Apparently they were showing both the 3D and 2D versions in the same auditorium. So the 1pm showing was 3D, and then 2D at 4pm, 3D at 7pm, 2D at 10pm. Not sure why they did that. I ended up going to the 4pm showing and kind of regretted it. WAY too many little kids, including two brothers around 4-5 years old that sat right next to me, and their parents two rows behind... Those two little kids were annoying as hell. They kept talking directly to Rocket and Groot throughout the show. And then the mother, half way through the movie, came down a couple rows to ask her kids if they needed to use the restroom, very loudly, and they were ignoring her, so she kept asking over and over and over. Almost like the Stewie "Mommy, Mommy, Mommy, Mum, Mum, Mum!" scene.
I usually go to the showing closer to Noon, it costs more, about 2 dollars per ticket more, but it rarely has any kids, and usually is pretty empty.