We loved the gameplay and art style here! The alien-invasion idea was really fun, and provided for a really great gameplay loop.
Love the simple art style and the way that the upgrades impacted the gameplay, we just didn't feel like there were enough (the rules required 5 unlockable loot options, but there are only 3 - Big Laser, Energy X2 and Slow Motion) and they didn't impact gameplay as much as we would have liked.
We wouldn't consider the items that you are picking up during gameplay to be "loot", as you're not doing anything to "unlock" them and they aren't affecting gameplay except in that you collect them like currency to then spend on the "loot". Would be great to have a better sense of which items you should pick up to earn more points, like a cow being worth more than a small plant.
Or, as in Katamari Damacy, you could make it so that you can only pick up small items at first and then as you get further you can unlock the ability to pick up larger things that are worth more points with permanent upgrades that last until your round ends - with the player deciding whether to upgrade their ship for more points down the line or using a temporary buff to get more points in the short-term.
Overall, we had a great time with UFO Madness and hope you'll join us for our next Jam!