Whoever said John Cazale is so right. Genuinely one of the greatest losses to cinema ever. He made just 5 feature films in his short career. The Godfather, The Godfather II, The Conversation, The Deer Hunter and Dog Day Afternoon. All oscar nominated, all in the IMDB Top 250 and all considered classics by virtually everyone, and John Cazale had a big part to play in all of these films being great. His portrayal of the pathetic and childlike Fredo in Godfather II is so tragic and memorable. Breaks my heart that so many people don't even know who he is.
As for overrated: Samuel L. Jackson. He's made a career of playing the cool tough guy, but he has no depth and no range. Not saying I don't like him, because I actually do, but he is a one trick pony.