My take:
Bryan/Sheamus: Should have been on the main card, 2 on the better new comers of the past 2 years and a minor title on the line and they waste them on some undercard garbage.
DelRio/Edge: Why did this go on first? Shouldn't it have been later like title matches are supposed to be? Why did Edge win, what was the whole point of Del Rio's destiny storyline? The match itself was alright, but everything else about it was wrong.
Rhodes/Rey: Pretty much as expected, glad Cody won, since almost every other young gun on the card was buried.
Corre/Smackdown: what the flying f**k was that? A stable of younger guys who have been built to the moon and they get squashed by 2 guys on the way down, a glorified midcarder and a comedy jobber. Barrett and Jackson will both be main eventers in the future and in 5 years when we look back at their first WM we will see this garbage.
Orton/Punk: very good, neither came out of that looking any worse, feud certainly isn't over.
Cole/Lawler: Went on too long. A match like this should never top 10 minutes. Time could've been better used elsewhere.
HHH/Undertaker: Needed to be as good as their match 10 years ago to save the show. Probably was.
Ziglaycool/others: Basically got 4 current workers on the card so they could bring back Trish and let the midget do some flips. Pointless, would've been much better as 2 separate matches. More young talent wasted here (Dolph)
Cena/Miz: Disappointing match to close mania on. Heel/Tweener didn't really work in hindsight. Was glad to see Miz win (see my comment about Rhodes/Rey for reasoning), and I guess Rock laying them both out sent the crowd home happy. I don't know if the feud should go any further though, especially if the Rock is going away again.
All in all, disappointing Mania, had it's moments, but there was too many glaring faults with it.