it's tough to sum up why you need to read invincible in a concise post. here's a review of the first couple of trades. http://politedissent.com/archives/226
and my thoughts are below.
it's a great book that deals with growing up with superpowers, family life being torn apart by tragedy, choosing between women, and balancing life. sounds like a certain web-head, eh?
on the supes half, invincible's plot is open to danger that is larger than anything spidey deals with due to his powers. on that note, watching marks powers grow in the series is nifty. i always like it when heroes aren't at full potential when they first get powers.
another cool part of invincible is that the writer isn't afraid to totally fuck up mark(invinble)'s life. since invincible is a new property, he can do what he wants and not worry about other books, continuity, etc. this lets him do some actual life changing shit, not the crap that gets changed in a month that is standard fare at dc and marvel.
seriously, dude, i couldn't recommend this book more. you owe it to yourself to read it if you're a spidey fan or even just a comic fan. it's fun, action packed, and dramatic. pick it up asap.