I'm super impressed that you made everything from scratch, that's definitely a lofty goal and I think you did a great job with it. As for some feedback, the biggest thing I think would help in the difficulty area would be adding some type of enemy indicator to know where they're spawning in at. I felt like it ramped up pretty quickly and there usually wasn't enough time to cover both sides effectively. Maybe a little mini map?
Awesome work, hope to see you expand on it!