For me it depends on the band. Some bands are only fun live, because, while they are not so good on the record, their music is great for just jumping/moshing/handbanging around and it is a lot of fun with friends. Others are great live as well as on record, I just love to experience their music live. As BAN said, you can feel the music better, hard to explain for me, just a lot of endorphines flowing around for me . A good visual show is not so important for me, I like interaction with the audience and a great atmosphere, but fire shows or the like are not a must for me. I enjoy them, of cause, but I would enjoy the gig without proberbly as much.
So for me it mainly getting lost in the music one way or the other. Neck pain is the best indicator of a good gig the next day, since I usually prefer headbanging to moshing, too. Depending on the fans, a pit can be great, too. But I am more for moshing WITH each other rather than AGAINST each other. It is a way of dancing for me, not a fight. Might sound untrue, but I never liked the people who actually start beating or purposely hurting others in the pit.