There isn't much content, but what is here is very high quality. The art all looks top notch and is animated very fluidly (aside from obvious placeholder red and yellow blocks). The scan lines are also the nice touch. The sound effects all fit well and have a nice genesis sound to them. I guess some music would be nice but when everything else is so good it's hard to complain.
For what little there is the gameplay is very fun. The platforming controls and the shooting controls both work well. I really like how there are several different weapons to pick up and choose from - they add some nice variety to the game and they're all quite fun to use. Having the power-ups always swap with the weapon you're not using is a clever idea. It gives you some selection over the weapons you have and means power-ups don't interrupt you when shooting. The only minor issue is that the enemies are a bit lacking but you can't really expect super complex enemies in such a short time frame.