it takes a bit to get going. If I could go change one thing it's be the chances to spawn more spawners. It takes around 5-6 minutes to really start getting what I would call "out of control", it gets nearly impossible at the 8-10 minute mark, depending on how you play. You can be surrounded by around 200 enemies consistently at that point and past 15 minutes which I've only made once without exploiting a glitch you can barely see the level.