There are 4 types of genres that play significantly better with a mouse and keyboard
1. Shooters
2. RTS
3. Isometric RPGs
4. Point and click
Pretty much everything else either plays better with a controller or works fine for either control scheme.
Fighting games, hack and slash, character action games, all play significantly better with a controller.
Is there a specific type of game you're looking to play? Are you only asking about PC exclusives or do you want to know about all PC games in general?