There's nothing in BL1 that's worth playing after BL2. There's no story to really catch up on, and almost everything was an improvement in BL2. Some people don't like the change in some classes but that's just because they were used to the old way. IMO people who think the first is better just remember it fondly because it was fresh and new. BL2 is very much more of the same so the honeymoon was over, so to speak.
Thanks for the info. I'm in the same situation as the op; I bought BL2 without playing the first and was wondering if it's worth playing BL1.
Right now, I'm at level 30 so I assume I'm a little over halfway done. After I beat the game, Dishonered will be out and I'll be playing that. After that comes Walking Dead Episode 4. Once I finished that I planned on playing BL1 (assuming I can snag it for 75% off) but am considering skipping it and just replaying BL2 with a new class and getting into multi. So is the general concensus that a replay of BL2 is better than playing BL1 for the first time?