thanks for your request.
Firstly I'd like to say you've done a good job on this game considering your experience.
Although the game is reasonably playable it is not yet of a standard I'd consider ready for the showcase.
However you've got most of the basics down and with a little bit more work, I think you can get it to an acceptable level.
Heres some feedback that should help you move the game in the right direction.
1) The lack of sound really harms overall quality, not hearing anything when a laser is fired or character jumping or completing a level is disappointing. Its pretty easy to add some basic sounds I'd recommend you have a look at SFXR
, you can generate your own sound for your game.
2) Debugging Code such as System.out.println() hogging the system, on less powerful systems the lag is especially noticeable. The console should not be outputting masses of data.
3) Blandness. The game is very bland and static, try to break this up by having some sort of animation or other details happening. You have nice splash screens between levels but they are static and could do with some animation. In game the tiles of the background are all the same and could do with some extra detail to break this blandness, Brackeens
book has a nice section on how you can have the odd tile to achieve this.
4) Sub Goal to Gameplay, I see you only have the goal of killing aliens, but add some more aspects to the gameplay like collecting coins or other powerups, leave these as optional, it makes for a more deeper game.
5) Achievement, the feeling of making progress in a game makes for a more addictive and interesting experience, reward the player with a level complete screen showing what he has achieved in the level or how fast they completed it.
6) The little touches, add lots of small touches to the game, something for example that'd make the player grin, like the alien doing something funny when shot or the player animation when standing still. Can make the game more interesting.
I hope some of this feedback is useful, keep up the good work.