I have played over 30 COMPO games, and for some reason or another I felt that these are two gems that should not be overlooked. I wouldn't be at all surprised to find them in the top 10 in the final score.

Deliver Us From Evil by @candlesan

It's a shooter in which you have to prevent the zombies from touching Delina's spirit. In case the cooldown of the shotgun doesn't give you enough time, you can use flares on Delina to give you a few extra seconds to kill the zombies. It may seem like a simple approach, but it's all so delightful, the sounds, the setting, the lighting system, the particles... it's all part of an experience that you can't put down until you've beaten the game. And once you get through it, it leaves a lasting impression (a good indicator that something has been done right).

Play it here: https://ldjam.com/events/ludum-dare/53/deliver-us-from-evil-1

earthmover by @dishwand

This kind of sokoban is self-explanatory once you start playing. You flip a machine, in which you can only push the blocks in a certain position. But everything is so polished, the control, the graphics, the lines of dialogue (you can feel a personality of the machine operator and a backstory that goes back to the moment you play), the exquisite sense of humour, the sound, even the increasing difficulty of the puzzles (which you can overcome if you put some time into it), everything again makes a lasting impression when you beat it.

Play it here: https://ldjam.com/events/ludum-dare/53/earthmover