Good for first game, needs improvements
I want to start out by saying congratulations for finishing your first game! I enjoyed it for the most part, and think that you should keep at learning the program.
There were several parts of the game that I felt were lacking, though. For one, the player and enemy movement seemed a little too fast. I would have enjoyed it significantly more if it went at a more "arcadey" pace.
The enemy patterns were pretty predictable, too. There didn't seem to be a terrible amount of variety in the way the enemies moved, which removed some of the challenge. Part of the fun in most games is slowly weening the player into a new enemy type, and having the player learn the typical pattern, and how to get around it.
Level design is another biggy. I'd be fine if you just left the flat floor pattern the same, but perhaps scatter various obstacles or barricades around, decorate each level to give it its own unique flavor. Enemy arrangement alone does not a good level make.
My final gripe is with the final boss. The shooting pattern was completely erratic. There was no way to predict where she was going to shoot next, removing any sort of strategy element from it. I would have enjoyed it much more if the final boss were to have a consistent shooting pattern with a varied (but predictable) movement pattern.
Take a look into doing some of these things for future games of yours, and I assure you, you'll get tons of satisfied players.