Anyone old enough to appreciate the PC game Pipe Dreams (or Pipe Mania) will get a nostalgic kick out of Cogs. The game focuses on sliding pieces (pipes and/or gears) together to connect steam pipes, ring bells, fill up balloons, or power up machinery. The puzzles are clever and have a lot of variety. In some levels you work on a flat surface, while others have you rotating a cube to connect multiple sides.
The levels in Cogs also get challenging rather quickly. Within the first 5 levels you'll feel like you're solving an actual puzzle instead of walking through a tutorial. The game features 50 levels and 3 different types of play. For 5 to 10 bucks on Steam I'd say it's great for puzzle fans.
Also if you like Steampunk themes there's a lot of that in here too.