Operated by typical Boyz, the BS is 2. Armour is F:11, S11, R:10. It's not great, that's for sure. Especially compared to the likes of a Battlewagon or a Deff Dread.
I assembled this guy before the codex came out, it had been sitting on my desk for a while. If I had waited, I wouldn't have had a Stikkbomb Chukka on my Boomgun-Wagon ... as there's no passengers to pass the benefit to, so it's purely cosmetic on this guy.
Also, since I am collecting an Evil Sunz army, I will take Red Paint Job to keep things fluffy. When my Lootas go a little crazy with pulling the wrong levers they'll lurch forward an extra inch. ;)
I think my favorite detail on the wagon is the pistol mounted to the side of the turret: