You deserve it after how awesome you were, and you comparing it to Alien Syndrome, a very underrated game that I loved, is going to get me to try out the demo.
Well, the comparison is only that both really scratched my co-op top-down hack-and-slash urge. My brother and I are a little more than 4 hours in I think and have beaten ranks C, B, and A now. Rank S awaits, but I think we also get to unlock and play a mode with more than just the original 150 pkmn? Anyways, we're having a blast. I think it would really be not as fun without a second player, because two players can choose complimentary pokemon/strategies and cover each other's back. For example, if my brother is using roll out to just blast through hordes of enemies, I can just keep running after him and mopping up the occasional straggler. OR he can be oddish, I can be gloom, and we can just set up a front, using a ranged poison spread attack to lock down an entire corridor of enemies slowly advancing on us.
It's worth trying the demo to see if you could be a fan of that sort of experience.