Prototype is one of my favorite zombie free roam type games. The story line was mysterious and quite interesting. The concept of the game was phenomenal, and I did like how there was different upgrades, powers, and abilities you could unlock.
Though while I was okay with the main story missions, I often did get bored from the side missions. The side missions would usually be just trying to kill someone and gain their memories for your upgrades, destroy a base of infected, or just destroy the military base.
Some parts of the game can be annoyingly challenging or just downright unfair in a way.
However I highly do recommend the game for players who enjoy zombie games while also enjoying destroying the environment around you.