Rather fun game, however after a second playthrough it becomes rather apparent that the merging of weapons is much more of a predetermined thing as the weapon drops are always in the same order, and you cannot skip a drop and then pick up the next weapon. There are also a couple of spots in the map where the player can funnel all the zombies with very engaging gameplay (the bottom left house being one of them). Lastly as the zombies spawn in certain areas, regardless of the players location, you can essentially become telefragged if you accidently stumble into one of the places.
However the gameplay as mentioned is quite fun, and overall this would really just benefit from a bit more though out map design, spawn mechanics, and larger arsenal that allows players to actually make choices on the guns that they want to merge. The music as others have mentioned is near inaudible however, which is kind of underwhelming.