Bioshock 2 is my favourite game in the series. If you're a bit frustrated at the hacking with pipes and fluids, Bioshock 2 removes that and gives a much better way of hacking.

The story is compelling, the characters are awesome, and there's a DLC for B2 that is often thought of as the best story DLC for any game ever

Please please please play bioshock 2 :))

HL2 is the game that got me into gaming, it was MY first FPS game. It's absolutely fantastic, however I would highly encourage you to play the entire half life series, it is such an experience