Battlezone is a fun first person shooter on the 2600. I think you'd like it.
Adventure is a fun game that a lot of people think might have inspired the original Legend of Zelda game. You get to explore dungeons, castles, and catecombs, to find a magic chalice that was stolen by an evil magician, and you must collect items to aid you on your quest. One of the items is a sword, which you must use to kill the three dragons sent by the magician. You can also collect keys to unlock castles. There's a bat that will steal items from you. You can also only hold one item at a time, adding a challenge.
Yars' Revenge is one of the best games for the 2600.
Jungle Hunt is a favorite of mine.
Pitfall is a classic that I'm sure you'd enjoy.
Ms. Pacman.
Jr. Pacman.
Asteroids.
Many, many games.