The strongest aspect of the movie is the interaction between Robert Downey Jr. and Val Kilmer. Their characters are already funny and interesting on their own, but it's when they're together the movie really shines. The differences between these two characters make for such hilarious banter that one can't help but to laugh out loud whereas most movies with similar kind of witty banter merely make you chuckle. The banter is however not the only hilarious aspect. There's also Robert Downey Jr.'s narration which breaks the 4th wall so often that by the end there's nothing left of it except crumbs.
Even though I keep hammering in how funny this movie is, don't go into it thinking that's a pure comedy. Because it's not. It may have plenty of comedy, but it has no shortage of action, mystery and drama. It's also very effective in those areas. It's very well rounded and it's the kind of movie I think a lot of people will love, and those who doesn't will at least enjoy it. I recommend that anyone why hasn't already seen this should go watch as soon as possible.
Despite my so far never ending praise for this film, I'm not going to give this my highest score because it somewhat lacks what my all time favorite films have - re-watch value. Granted, I do still like it despite that this is my third time watching it. But I don't love this time around. It's incredible on the first watch, but - like I said earlier - it loses a lot of it's edge after that.