I liked this a lot! Running over the zombies and whacking them with the barrel of the tank felt great, and I can tell a lot of work went into the effects in order to bring that feeling to life. I honestly had more success using the barrel as a club than I did shooting with it, haha. I also really like the aesthetics and the little details you added, like the treads leaving a path in the snow behind you.
I'm not very good at mouse and keyboard controls, so getting around was a bit of a struggle, but as other people said, I think that adds to the fun (to a point). I know it's a skill issue, but it was a bit frustrating to feel like I couldn't really control where I was going. If you continue working on this project, perhaps you could add a tutorial stage that makes sure players have the basics down before letting them get into the rest of the action?
That's a pretty minor blemish, though; otherwise, great work!