MDK2 (released in March of 2000) had you play a third of the levels as a four-armed anthropomorphic dog and respectively let you hold four weapons at the same time. The gameplay balance they were going for was similar to Serious Sam, I think... i.e. everybody dies in large numbers (except you, occasionally). Actually, that game was made up almost exclusively of cool new features, go play it. The fact that one of the best third-person shooters/adventures was produced by BioWare of all companies still blows my mind a bit.