Sonic? On PC? Hmmm. Not my idea of relaxing mouse clicking, lol.
I can't pick a specific favourite PC game, way too many to mention.
What I will mention is:
Robin Hood - The Legend Of Sherwood
Because I'm sure there's many people here who have never heard of this amazing little gem of a game, let alone played it. (Rating: 8.6/10 - Gamespot)
This game has everything you could wish for from a simple isometric sword-and-quest based action adventure. It's basically a CRPG with no levelling or hyper-magic etc.
Here's a youtube link to the end-of-game video:
Robin Hood Legenda Sherwood - Secret Ending (polish version) - YouTube
Best viewed on full screen and don't worry, there is no spoilerage from watching this clip