They botched many arcade ports on the 2600,it just didnt have the power to make those games look right. Dont get me wrong though,some of those 2600 ports are classics in their own right.
In fact,I prefer Asteroids on the 2600 over the arcade version.As for Berzerk,my favorite port of that game is on the 5200.As far as Pacman on the 2600 goes,well its just better to not discuss that game...I still feel the burn I got when I got that game as a kid.