Weirdly, if you look at it from a purely price-per-hour-of-enjoyment perspective, the two all-time champions in my library are probably Vampire Survivors and Hot Dogs, Horseshoes & Hand Grenades.

You couldn't pick two more different games, in virtually every aspect. One is a minimalist, top-down autoshooter game that established its own genre. It cost me 3 dollars in Early Access. It has come out of Early Access, with flying colors. I have spent 170 hours in it. It is a poster child for the "came out of Early Access as a huge hit" phenomenon.

The other is a VR-only firearms simulation sandbox game, with a whole bunch of different game modes, thousands of meticulously simulated weapons, and a wiener fixation. It entered Early Access in 2016, cost 20 dollars, and is still in Early Access. I have spend 502 hours in it, and it's by far my most played VR game. It exemplifies a weird third-way philosophy, where a game is literally constantly updated, throughout the Early Access period, to the point that it really doesn't matter how long it remains in Early Access, because anyone who even vaguely enjoys it has spent so much time in it, and gotten so much value from it that...well, it really doesn't matter if it ever releases, in ANY state.

BeamNG.drive is another example of that sort of game. Because I'm a weirdo who plays weird sandbox games, it should be no surprise that I also fuck with that game. Although I didn't pick it up until a couple months ago.