Beat Saber is a game so simple that I didn't even need the rules explained except for a few obscurities. And yet it has enough depth to be played for years, has no unfairness whatsoever, and it's hard to think of a single thing to complain about.
All of the 36 built-in songs are very well-mapped; they avoid monotony and have good progression (later patterns often build on earlier patterns, keeping the song fresh despite consistent motifs). They also have a remarkably consistent standard of meaning for each of the 5 difficulties, apart from the 6 Camellia songs which are way harder but have their own consistent standard.
It strikes a good balance with song length with most being 2-3 minutes, and with the health system: you lose about 1/7th of max health for a miss, 1/10th for a bad cut, and gain about 1% for each hit. These balances make the game extremely satisfying to play, win or lose.
Even the songs themselves are good! Heck, I listen to some of them outside of the game. I think my favorite is Escape.
It has very high replay value; the songs can be taken past Expert+ with the practice mode which lets you adjust the speed, besides choosing how far in to start, and there are modifiers like "disappearing arrows" which can offer a new challenge. There are also the alternate modes: single-saber, no arrows, and 90/360-degree modes. But I don't think much of those, because they don't seem to really remix the experience much, and most of the songs only implement them for low difficulties. Finally, there are mods that enable commnuity-made maps, including an AI to generate maps for any song.
Beat Saber features a "multiplayer", but it's not very interesting because it's of the "you just play at the same time with no interaction and compete for score" sort. And speaking of score, the whole scoring system feels unsatisfying to me because it's based on an objective I never even think about outside of multiplayer. You get more points for hitting in the center of blocks and for swinging a wider angle to cut them. This has nothing to do with whether you pass or fail a level, and that's why I don't like it: to me any game that has winning and losing is a game about winning and losing; as soon I can beat a level in the first place, I move on to a level I can't beat instead of trying to get a higher "score". Fewer misses doesn't even necessarily mean more points.