At the screening that I attended of Guardians of the Galaxy, a 2D screening, there were subtitles on screen. Cinema goers quickly voiced their complaints to the staff at Southampton Cineworld, stating that the subtitles were a distraction. The cinema staff were quick to act and well, in my mind, acted as fairly and as appropriately as they could, providing customers with a choice of either a free ticket for a future screening, and a refund, or an option to watch a 3D version of the movie, and to be supplied with free 3D glasses.
I chose to accept the 3D glasses and watched the movie in 3D. The upgrade took the movie closer to the format in which I had originally intended to watch the movie. I think that the film definitely benefits from 3D, and I can imagine that watching the film on IMAX would be well worth it too!
So maybe it's just coincidence, but seems like there has been a few problems with the screening of this movie, even if the quality of the movie itself can't be questioned; an excellent, action packed and quick witted, movie.