You can pick up enough to learn about the Ascendants contextually in the second book. The groundwork for the ascendants is pretty solid by the middle of the second book, hard to go into without a major spoiler concerning Shadowthrone though.
I'd REALLY recommend this series to anyone that's a fan of epic fantasy, though not ahead of ASoIaF :P I didn't find out about Malazan's origin as a shared world till after hunting down the newest volumes on Amazon, but that's where I was getting the crummy "high fantasy vibe". But at least Malazan wasn't just some machine-written AD&D campaign drivel, it has much loftier pedigree: it was supposed to be a GURPS world
