You guys need to get Shadow Warrior 2 - it's freaking awesome. It's like the first one on steroids, with loot, missions, skills and - most importantly - 4 person co-op. Great melee system and bad-ass weapons, plus you can tailor your character to the way you play. This one could be great fun to play with 4 of us and I reckon you would all like it. As Wang himself says... "The way of the Wang is long and hard... and ribbed for her pleasure".
Get it bought.