Live is mainly different because of the way its set up. Live is based on triggering loops and pieces of audio or midi. Ofcourse you can record into it, and sequence everything like a normal sequencer, but really the core of it is triggering audio. This allows for more of a play type feel.

Live also allows you to midi map almost everything in the program, so if you have a playable midi controller(knobs help) than manipulating effects via midi, or triggering audio or midi events via midi really becomes more like playing an instrument.

Most sequencers aren't set up like this. The midi mapping is really where its at.

check out the main ableton site for more info, and if you haven't already, download the demo.

have fun