Both are equally enjoyable but the HE500 is more fun, the notes sound sharper around the edges, and vocals are more emotive than the dryer sounding but still good vocals on the LCD2s. I always felt LCD2 excelled w/male vocals. The LCD2 reigns supreme when it comes to texture/timbre and is a bit warmer/natural sounding to me. They both have a clean, crisp sound, with the HE500 having a touch more clarity b/c of the treble emphasis and lesser bass. Having heard both it's hard to choose one over the other. But if there's anything that would make me choose the LCD2 over the HE500 it would be the timbre/texture, which is more important to me than other aspects. LCD2's timbre sounds more fleshed out and better articulated. I feel like I'm extracting more out of the music. And if there's anything that would have me choose the HE500 over the LCD2 it would be the overall sound/notes being more sharply focused/defined and the ability to portray emotion in the singer's voice for a "wetter" presentation.
People say the LCD2s bass is way better and it probably is. I don't feel like I'm missing much with the HE500 in that area because it can still bring that low rumble when it's called for.