My Krieg is level 35 and I thoroughly enjoy him. The skill "Release the Beast" is particularly helpful. With it, I spend nearly all of my combat time as a badass psycho mutant. Wreck people as a mutant, and then when it's over, my action skill is immediately ready again. Hit low health again and then LB and the beast is back in the game! In the rare event I'm ever downed, simply detonating myself (Light the Fuse) close enough to an enemy revives me.
Also, the thrown buzz axe does great damage. The Warrior didn't stand a chance.
I really like Krieg too. I haven't finished PT1 yet though. But he's a blast so far. I'm going with a Mania/Bloodlust build and just wrecking fools. I really love his one-liners. I don't think any of the other characters have made me laugh as much as he does. Totally worth the ten bucks to me. :D