I recently watched Magnolia in the Prince Charles Cinema in London. I'd seen it multiple times before, but never in a cinema. The bit with the frogs was incredible, going from peaceful to absolutely deafening. That scene is now my most memorable.
There are so many movies I haven't had a chance to watch in a cinema, I wish more theaters would play classics on their largest screens. I just found out that one of our local cinemas now has weekly 'classic sneaks'. Lucky me.
I'm not going to tell you what movies you should like. Magnolia is a long film, and it takes a while to get where it is going. Some people think it's gimmick-y, others are willing to suspend belief and go with it. But either way, Julianne Moore wound tight, desperate William H Macy, lonely John C Reilly, Jason Robards on his deathbed... these are all epic performances (as is Tom Cruise of course). The secondary players as well -- Philip Baker Hall, Philip Seymour Hoffman, Melora Walters, Jeremy Blackman (kid), Luis Guzman -- are superb. I acknowledge lots of people hate Magnolia but if you found it forgettable, I doubt you were even paying attention in the first place.