I downloaded the RE5 Versus add-on from the XBL Marketplace too and only managed to get round to playing it last night with one of the lads from the
RE5 Forum. I think the Versus mode is a bit weak. I can't play it for too long before getting really tired of it. In fact, I probably won't touch it again after I've unlocked the DLC achievements. It is nice that you earn Exchange Points as you play, though. The extra points means I can finally get round to purchasing the Infinite Ammo option for all guns.
I wouldn't really recommend the Versus DLC, really, it might only be 400 MS Points but I can't see myself playing it for much longer. Resident Evil 5's co-op campaign is where the multiplayer really shines in my opinion.