Waves or some special menace would make it better
I don't mind a simple game, but this has a couple of issues:
- It remains constantly the same. More and more aliens come, and there are different species, but it just gets more intense each moment till you die. Waves would be one option to make it more interesting. Another option would be some kind of more specific and threatening menace that you're hoping to avoid.
- Once most of the buildings are destroyed you can keep the basic aliens away by just shooting a bit above the last building(s). That makes playing the game feel stupid.
- The big bombs felt very powerless. For the regular enemies they are just more unhandy to use, but surprisingly they didn't really seem to be effective against those stronger ships either.
- At least I often find it difficult to enjoy a game where the controls are very restricted. So since you cannot move the cannon, there should be something really special to keep the player interested.