A solo is be no means an essentail part of the song, and you dont really need it... It's actaully worse (i find), to have a routine song, with perdictable solo... Right I'm gonna say something against Gun's and roses, so hold on, right, Slashs solos are ok, but sadly they're over hyped to proposterous levels, and sadly they're quite cheezy... now if you look at a band like Radio head, and listen to the solo from "paraniod android", you'll see it's not preditable or cheesy, unless you've heard the solo from "just", which isn't too disimlar ... what I'm trying to say is that you can over do it with solos... Why not have keyboard or bass solos, or the hell with solos...
Anyway that's just my humble oppinion..