So, I give this movie 3.5 stars out of 5. It's good, but I felt the pacing was too quick, at the expense of character development of the protagonists. Also, I didn't really feel much for the villains. They were just there as a necessary device to keep the plot moving but I didn't especially hate them. Yeah, they were bad, but that's just because we are told they're bad. It's not as if we really watched them do much bad stuff before we are told they are bad.
Because of this, I found the plot, although in some ways simple, a little bit confusing in some other ways.
As for the presentation, I was pleased. I was in the "cheap" 2D room in a theatre where they were also showing it as UltraAVX in 3D, but even my cheap 2D looked good. Very good in fact. In some areas the contrast was a little light, but overall the tones and contrast was very good, with minimal noticeable pixelation. This was in stark contrast to when I saw Star Wars (Attack of the Clones IIRC) digitally projected for the first time. Digital projection back then (over a decade ago) definitely looked like a work in progress, whereas Guardians of the Galaxy made it look like digital projection has finally matured. I don't know if this is 4K or 2K, but I don't care. (UltraAVX is 4K, but apparently the screen is bigger too.)
I feel like this joke was missed by a lot of people. =(
It got quite a few laughs in my theatre.