The last Trek movie I really dug was First Contact back in 1996. This new one should go to any Trekkie/Trekker's Top Three.
It's also a film that non-fans - or those who've been out in the cold - will get a good kick out of. Each of the cast does a really good job of standing out to you, and the storyline doesn't feel hollow or contrived.
Bottom line: Believe the comparison to Iron Man because, like comic fans who went in weary of yet another sub-par comic book adaptation, you're going to be very pleasantly surprised.