It's hard to classify Bioshock, considering it's probably more accurately "Hydropunk" but it covers all the bases a steampunk game needs. Distopic society? Check. An isolated underwater Utopia inhabited by genetically altered super-humans? Well duh. Alternative means of power? Check. Cool high-gloss environments? Check. Cool 1940s weapons? Check. Giant mutant humans walking around in metal diver suits? Yessir.
If you haven't played Bioshock yet, crawl out from under your rock and go get Bioshock One and Two. They costs like... maybe a couple bucks now, and are available on Xbox 360, PC and PS3. And plus - it will prepare you for what's on the next page.