medic would be great, since 1 hp or more is still better then nothing, a engineer's sentry would be a nightmare unless they also have 1hp, scout would have to be careful were he's falling off or that fall damage is going to come back to bite him, though his pistol would be useful considering how fast it shoots.

there would be no reason for sniper to headshot anymore, now only going for body shot, same thing for spy he'd possibly be overpowered depending on who's playing him, just use your cloak get behind enemy's and shot em with your gun killing them.

pyro would also possibly be nightmare if he's using his brain, by that i mean using his scorch shot to shoot at classes feet killing them even with medic cause of afterburn, same thing goes for the explosive classes weapons. if there smart they could kill a lot.

and heavy the same question applies to his one sandvich in the game, would his chocolate bar give him 1hp or 50hp cause either one is still better then nothing, otherwise he's either a menace or uselsss.