Wanting (and not owning) both Pillars and NBA, I'm pretty happy right out of the gate. Overcooked looks like a lot of fun, so I'll try that, but the one I'm installing first is War for the Overworld, which looks heavily influenced by Dungeon Keeper. Good bundle for me.
Even though I'm skipping the next (own KF2), I want to cheerlead for it a bit. If you've only tried KF, or maybe KF2 six months ago or more, I'd urge you to give it another look. They've added so much content since it first launched in early access, and the gameplay has improved a great deal. There are some truly wacky Workshop maps to play if that's not enough. And, as fox alluded to, the Weekly Events have been a lot of fun: shrinking or growing enemies, special fleshpound waves, headshot-only, and they all come with rewards.
If you want a little variety, try the map called The Descent... It's a string of ten smallish maps that play out randomly. Tripwire hinted at making more maps like this. Of course, it's a horde game when all is said and done, so if that turns you off then the bells and whistles aren't going to matter. But if it's been a while, or you've never tried it, it's worth a shot.