Starting with the texturing, it is very very basic and the brushwork is very blocky. It just comes across as very amateur and looks like this is someone's first map. Spend a lot more time on making some more interesting brush work and getting some decent texturing in there. Use decals and sprays to really make the map look much better.

The displacements are OK, but you have fallen for a common mistake, trying to make a rectangular displacement, you need to use several displacements sewn together across the length of the map, this will help to hide sharp edges in the displacements.

The gameplay is basic, but the cannon does make it a little interesting and makes the map a little more fun to play. Though the cannon is really the only highlight this map has and it has been one before.

The lighting is boring and basic, get some interesting lighting in there and learn how to change the skybox texture too. A 3D skybox would help this map drastically in terms of looks if done properly.

Overall, it is a basic map, with nothing special, it doesn't stand out and has a lot of problems with it that need fixing. Just keep mapping and hopefully with each new map you will get better and better, try to keep learning new stuff to do in Hammer and you will be producing quality pieces of work in no time.