What's a niche/underappreciated game that lives rent free in your head

Was wondering what are some niece and or underappreciated games that won't leave others minds

The game that got me thinking about this was zombie u for the Wii u, but more specifically the vs multilayer mode it had

This was an asymmetrical vs mode where one player on the on the tv was playing a cod zombies style zombie survival game and the other played an RTS on the tablet controlling the zombies the other was fighting.

Had a lot of good memories playing this with my friends back in highschool and still remember it very fondly. A video I was watching recently was talking about canceled valve games and one of them briefly mentioned was a game called left 4 dead ar where it was the exact same concept and got me wishing valve expanded on it. The zombie u version was pretty clunky and unbalanced, but a valve version with source engine shooting and movement, as well as valve standered polish sounds incredible. Probably didn't make it far in the development cycle though since the only bits of this game we have to my knowledge is a former valve employee talking about it.