I know older titles are usually the topic in this community but a lot of the popular f2p games are getting pretty old now too, and if you're like me you've been curious about some of them and even pleasantly surprised now and again.
There are many examples like League of Legends, Apex Legends, Raid: Shadow Legends etc and I usually get hooked on one and play it for some months or more. I'm not really trying to get into the "business" side of things, I personally very rarely purchase anything but if you do that's absolutely fine too.
The current ones I play regularly:
PC - Enlisted - A WW2 shooter with vehicles like the Battlefield games. Same publisher and game engine as War Thunder and has been in open beta for over 2 years now. Kinda janky still but regularly updated and enjoyable.
Android - CUE cards universe everything (I forget exactly lol) - Fun deck builder but very grindy if you don't buy shit. Pretty unique concept for a deck builder what I've come across. Short games too so good for a smoke break or the bus or whatever.
Gumballs and Dungeons is a fun roguelike gacha. The main game loop is picking a Gumball which have different stats and mechanics and diving a Dungeon which has different enemies and mechanics. So you want to synergize your gumball with your strategy for a particular dungeon. Each floor of a dungeon is a 6x5 tile map and you flip the tiles looking for the down exit. There’s a boss every so many floors and just try to go a deep as you can. At the end of the run you keep some of the stuff you collected to unlock new dungeons and gumballs.
Another Eden is a gacha RPG from the writer and composer of sony enix dream team; chrono series, xeno series, final fantasy. There is so much content there and a ton of crossovers with other franchises. The map movement is done really well here for a mobile targeted rpg, it’s slightly elevated from a side scroll perspective and you mostly move horizontally in lanes with vertical connections here and there to switch between lanes. The writing is great, the music is great, the battle mechanics can get really deep.