For analytical thinkers, SpaceChem is hands down the best PC based puzzle gaming experience there is. Build, troubleshoot, and watch your solutions come to life. Then rebuild them with improved efficiency! It's a game that takes a lifetime to master, but there's really no wrong way to play. The majority of my solutions seem to take the Rube Goldberg approach, but they work and there's nothing more satisfying than seeing a working solution in action.
The 63 Corvi DLC provides a handful of additional puzzles and brings barriers and teleportation to the mix offering some serious head pounding challenge. Definitely worth picking up if you haven't given up on the base game already.