I was lucky enough to be just the right age (13) the summer both Star Wars and Close Encounters of the Third Kind came out. It was a double whammy I'm not sure I've experienced since. I saw them both seven or eight times in the theatre (and countless times since) and even the disappointment of the sterile 'prequels' has not managed to dim the love I have for Star Wars.
One of the most recent films that has 'blown me away' is Black Hawk Down. I came out of the theatre virtually unable to speak for several hours. I own the DVD, bought it the day it came out and still haven't watched the film itself all the way through because I wasn't sure I could put myself through that again. I don't rate Josh Hartnett much as an actor but here he was perfect in the role of Everyday Joe thrust into a situation beyond his comprehension. The grainy/slow-mo battle scenes that Ridley Scott experimented with in Gladiator came into full force in BHD, lending the bloodshed (I'd call them 'fight scenes' but they're so. much. more.) a gritty, confusing realism that thrusts you into the heart of the action from the participants' point of view, not as a distant observer.
Moulin Rouge is another one that blew me away and, oddly enough, it was only on the second viewing that I left the theatre in floods of tears, heartbroken by the tragedy and yet strangely uplifted by the melodrama of Christian and Satine's love and loss. The first time, I was impressed by the sets and the costumes and the dancing and all the flashy bits, and mildly saddened that there was no Happy Ever After, but it was only when I saw it again that I bought into the human drama/tragedy and decided that, it might not be the best film I've ever seen, but its one of the ones I love the most, despite its flaws.
Other honourable mentions go to Wim Wender's Wings of Desire (Der Himmel über Berlin) and Jim Jarmusch's Down By Law, both of which use black+white film to effectively sustain a certain kind of atmosphere (in Wenders case, the angels live in a beautifully stark B&W world until they 'fall to earth' and experience both the joy and pain of a colourful mortal existence). I saw both of these in theatre and am glad I did.
Most recently, I snuck into a showing of Cold Mountain directly after seeing Tom Cruise's The Last Samurai with my mother. We neither of us had anything to do so, after a quick bathroom break, we thought we'd check out this civil war romance while the ticket attendants weren't looking. Twenty, thirty minutes in and I was desperately hoping my mum wasn't going to turn to me and suggest we'd got our free preview and it was time to leave. Instead she leaned over and whispered, "My God, this is so much better than the last one." We stayed until the final credits rolled. Oddly enough I think I would have quite liked The Last Samurai if it hadn't been so thoroughly upstaged that night by a far better crafted film. Cruise's histrionics and posturing threw into highlight Jude Law's subtle and moving portrayal of Inman and Minghella's glossy but brutal portrayal of the Civil war and its violence made TLS look like just another Hollywood action flick, only in costume. In retrospect, I don't deny that Cold Mountain has its flaws but, I have to say, it 'blew me away' that evening.