It's very polished and pretty fun although very difficult. You have so little time to prepare between rounds. Only managed to get a few things setup before the timer ran out. Getting the sentry guns out became my top priority, since they let you focus on other stuff then just fighting during the rounds. Did encounter a bug where my crystals were still being attacked if you killed the last enemy while its attack your crystal. So be wary of that if your playing.
Also tip for others, stack the ammo boxes. It lets you reload faster