He's a good actor and a great leading man. He doesn't have the most range but when you need his tough-but-not-too-tough-sarcastic-everyman-who-can-take-a-punch.
Hudson Hawk is one of my favorite movies ever made.
postscript: I just realized he's actually credited as a co-writer of Hudson Hawk!
I watched Hudson Hawk for the first time a couple years ago and it's one of the most fun, insane, over the top weird movies I've ever seen. Even stranger knowing that Bruce Willis had wanted to do this cat burglar character for years prior.
I don't even know what comes close as far as times I've said "What the fuck?" while watching a movie. It's great.