Emo has much simpler riffs then metal and thus you're probably more free to do insane stage antics and so on :)
If you want proof get me the most complicated emo riff you know and i'll be able to beat it hands down with a metallica riff.
Of course music shouldn't be about how complex or fast something is, but never-the-less that's the direct comparison between the guitar side.
Emo vocals are a lot more emphasized then metal vocals as emo songs are driven primarily by lyrics. Therefore the guitar work is probably going to come second to vocals. Metal is generally the opposite and guitar work is put above vocals (i'm talkin shred metal here) so for example Metallica's master of puppets - if you put those vocals in front of a monotonious riff of just powerchords it wouldn't have been a good song at all, but it's riffs made it amazing. put emo vocals infront of a monotonious riff of just powerchords and you've got a decent emo song :)
