You should be working on your skills in different genres of game so you can become a more well rounded gamer. If you just build up your FPS skillset, you'll have no platformer, RTS, racing, RPG/JRPG skills and when you start a new game you'll need to learn from the bottom all over again. A rather frustrating proposition.
You should do the same thing kids who are new to gaming do. Start 4 or 5 games from different genres, and play through them all at the same pace. Some games are too hard for most people to finish. Some people get stuck at a certain puzzle (not an issue with Google, but it used to be) and don't finish.
I suggest an FPS (you have one), an RPG (fallout 3), an adventure game (Batman Arkham Asylum (not a hard game) and a racer (one of the DiRT series). All these games are quite cheap now but still have modern graphics (except FO3 which looks a little dated).
It may seem like a lot to take on, but you may well find that you enjoy a different genre of game better than first person shooting and abandon HL2 altogether.
Just my 2 cents.