Fun game overall. The multitasking feeling of shooting and running around collecting health is really tense and dynamic.
Big problem tho in my opinion: each zombie takes two hits to kill, and each life drop gives one life back. which means, it's not really and "infinite" game, as you eventually will die even if you take 0 hits. Maybe the health pickups should heal for two, and then you can stay alive for as long as you take no hits.