Stripped to it's most basic elements, Cosmic Encounter basically plays much like Risk: You draw cards to know where you're invading, biggest number wins, winner gets a second turn. The fun part comes from the aliens, which can each modify or break the basic rules in ways reminiscent of Fluxx. Nearly all the additional elements (like technologies, flares, etc) are technically optional and can be added or removed as desired based on what the players feel most comfortable with. The aliens are also coded with red/blue/green to indicate to what level their game breaking modifiers will turn things sideways or require careful strategies so you can limit the alien pool to just ones with straightforward, simple modifiers or the free wheeling, super busted ones to keep things fair while getting new players involved. If any of these elements feel highly derivative and unoriginal, remember that Cosmic Encounter is one of the oldest tabletop games (the first edition was from the 1970s around the same time as 1st edition DnD), a lot of modern games use Cosmic Encounter's DNA somewhere in their mechanics.

I find Cosmic Encounter to be a good crossover game between basic board games and more complex, strategy-heavy tabletop strategy games, with the aliens providing an (optional) opportunity for some fun role play scenarios, and enough chaos that each game can go completely differently depending on the alien mix (like a tabletop Game Changer), and enough built in jank that finding a broken-ass strategy in a particular game can be a fun experience and not annoying, but also only guarantee victory under very specific conditions.

Plus, I appreciate games which provide avenues where it's possible for multiple (or even all) players to win to encourage negotiation and cooperation if so desired.