I played a couple of games with a friend's box. We failed March the first time, but we managed to beat it on the rebound. I wasn't there for the effects leading up to March, but it definitely made one portion of the game really difficult for us.
I love the idea, but I'm a little wary about getting Pandemic Legacy. My friend said that after you finish up the year-long campaign, you can't play it anymore. With Risk Legacy you can keep playing on the blasted board after those 15 games and I suppose keep changing the board until you run out of stickers.
But then I suppose that you're guaranteed at least 12 games of Pandemic. At $60, that means you're paying no more than $5 per game, which is still rather cheap entertainment. I'm still hesitant, but I did have fun with the two games I did play. And my Monday night RPG session lost some players, so now we have a four-person board game night. This game would be perfect for it, especially since one of those players hates Risk and refuses to play my Risk Legacy even though Legacy made it no longer Risk.