So, I unlocked a ton of achievements this week. I got a bunch from Battlefield 2 and Bioshock 2. All I did was play through Bioshock 2 and achieve rank 40 in the multiplayer. There are a few tricky multiplayer achievements, but the majority of Bioshock's achievements are easily obtainable through time. 
 
As for Battlefield 2, the singleplayer achievements don't add up to much. Most of them are multiplayer-focused as is the game. Simply unlock weapons for each class, fully upgrade at least one, and reach certain ranks (usually in 10's) and you'll get a good amount of them.