Transformer
Explorer
I think my only rules-based deal-breaker is if the DM insists on rolled hit points. I had a very long spell where I never rolled anything above a '1', and while playing a character with a weakness can be fun once, it very quickly ceases to be.
There's a rule, I believe in one of Kevin Crawford's games, that has you roll for hit points, but you re-roll your entire hit point pool at every level, and take the new result only if it's higher than the old one. I always thought that sounded like a good system. You get the randomness of rolling, but while you could get screwed for a level or even two, you're never permanently screwed. Eventually you will roll better, and your crappy rolls will be wiped from the record.