Do you remember Tooth and Nail? I played the version with Urzas, never really got the cloudpost one. Good times.
It's definitely ahead of the mana curve. Pack 4 of those in a deck and the other guy doesn't have a chance. 4 Hymns, 4 Ostracize, some Abyssal Specters...unless he's playing Goblins of White Weenie or some shit where he can flood the table with creatures before you blow up his hand, he's fucked.
It's not terrible. It's just that in my experience, a discard deck typically whittles the opponent's hand down really fast and then they don't do much discarding. The effect of a discard deck is really to limit the opponent's options, rather than simply to make them throw cards out. Therefore it'd be pretty slow to kill with Megrim. Again, it's not terrible, but those spots could be used for more effective cards...off the top of my head
4 Terror
4 Ostracize
4 Abyssal Specter
4 Dark Banishing
I'd run 20 swamps, but I'm paranoid about mana screw. You could go 18.
That brings you to 34-36 cards. 24-26 spots left. At least 6 go to discard spells, you'll want some more creatures as well. It's also not a terrible idea to run some Drudge Skeletons or something in case they get creatures out and you need a blocker. You'll also want some more removal, probably. And of course a win condition, probably something big and ugly. Yyou could go for a big Corrupt or Drain Life...I always liked Promise of Power cause it offered more flexibility.
Basically, you can go a lot of ways with the deck, but there's always gonna be a better choice than Megrim.