I started an Athena, but decided that I didn't want to worry about oxygen so much, so I went wtith a Claptrap further than any other charater. It's good to know other characters are fun. Sorry for the multiple replies, I really should have multiquote-ed.
Oxygen is rarely a major issue. The game is pretty good about putting air vents nearby and having enemies drop air tanks.
What I meant was, is the end game scaling so out of whack that it revolves solely around being forced to use a single game element?