Hello my friend. I just tested your game.
First of all, congratulations!!!
I know how hard and time consumming can be creating a game as a “Lone Wolf” 
Your game has potential, and if you polish your game more, it could become a very good game. But it seems you don’t want to work on UDK anymore. Anyway, I will give my observations, please take them as constructive criticism.
1- I loved your map, it is huge, beautifull, however, it is empty and it is not well optimized. I would rather prefeer small maps with more details than huge maps with not too much details. Also, you could use precomputed visibility volumes to help with performance and optimization, as they occlude parts of the map which are not seen by the player.
2- The character model looks good, however, you are using 100% default UDK Animations. Is not that hard to replace the default UDK Animations by your custom animations. I am doing this on my game: New PC, PS3 and Xbox360 Game - Fursan al-Aqsa - Knights of al-Aqsa Mosque - UDK Projects - Unreal Engine Forums
I am not changing the AnimationTree, I am following the same UDK AnimSet logic, the same animation names, like idle_ready_rif, rif_fwd, I am using the Aim Profiles Animations, however, just replacing them by my custom. They are edited MOCAP animations (some I purchased cheap from TrueBones, other I have done by myself with a kinect xbox360 camera), and they look far better than default UDK Animations
3- You should have more weapons (you can purchase many weapons packs on 3d marketplace by a very cheap price), and also a Reload System for your guns.
4- You could add some hit reaction animations on the zombies, to give a more “impact” whenever you kill them.
5- I liked the bloody screen whenever player gets hit. I have done the same in scaleform, inspired by Resident Evil Revelations 2
6- Also on the gameplay side, you should place the ammo on more easily accessible areas for the player. I have found just one ammo. I could not find any healthpack
7- Last but not least, your game is good, but can be better if you take a time for polishing it more.
Cheers and good luck!
