I've said it several times before - I don't like Leonardo DiCaprio's acting (he doesn't win me over in interviews either). I find him incredibly boring, put on, and just not that good. I'm in the minority, and Hollywood disagrees, so it is what it is... but I think he's more hype than actual product.
And I think his performance in What's Eating Gilbert Grape is what people are really thinking about when they consider his acting chops. It's completely different from any of his major roles that he would later play (he's typically stuck in Jack Dawson type roles... which is predictable and stupid, but when that comes easy and the money's good...).
I've only watched the film a couple of times - it's one of those movies like "Dan In Real Life" or "Elizabethtown" that's well done but kinda depressing (even if there are happy moments). But, DiCaprio's performance has always stuck with me. That kind of acting I can get on board with. He was totally committed and transformed into the character, whereas these days he transforms all the characters into himself and it's just meh.