Sounds like you might have issues with large field-of-view. Halo was designed to be played from a couch looking a TV somewhat far away, so it has a fairly narrow FOV. I know that at least some of the games you listed (Portal, Portal 2) have configurable FOV. Portal in particular also introduces a particular kind of motion blur to deal with the high-speed movement and rotation in that game, and you could have issues with that.