Decent. There needs to be an overall goal involved. I didn't find the upgrades to be overpriced, only took a couple of rounds to save up for each on which isn't too bad, but there definitely needs to be more of them. I feel like it does need to get harder the high you get. It's just as hard at the beginning as it is at 10,000. I could have just kept going but go bored of it.
Thanks. I am lowering the boss spawn rate more so the incentive is shifted to Metamorphosis to gain enhancement points.