Hey, have you ever noticed that the Chainsaw is pretty much the least used weapon? It's melee, and in a world of rifles and guns, being melee kinda stinks.
So, I propose...
A ricocheting effect. Everytime you click the fire button, or every 1 second the chainsaw is running (which ever is faster), you will deflect a bullet. This will not protect against explosives, and bullets from behind/top/bottom.
I know, I know, a chainsaw can't deflect bullets! But when has Soldat been realistic?
Damage increase. This, I think, is pretty important. The Chainsaw does not register well, and when it does, it only takes away like 9/10's of their life, and although that may seem to be a lot, keep in mind that it takes like years to actually get a chance to get up close.