Made it to wave 9, it gets very difficult to avoid running into newly spawned enemies at that point. I like that there's enemies that stand still and shoot at you in the later waves so have to adjust your movements to avoid them (I also enjoyed how the ghosts look embarrassed when you damage them). The online leaderboard is a nice touch!
Creative way of seeding the randomizer, reminds me of the Worms games where you could type in a word to always generate a specific level. To be honest, I entirely forgot to seed the randomizer in my own game so the initial wave of enemies is always identical but since I have lots of different places where random numbers are used in combination with the player input there's eventually enough entropy that it doesn't matter all that much anyway.