Personally I recommend Old School RuneScape.

Pros:

• F2P mode is robust enough to enjoy casually
• Membership is $12.50/month and drastically increases the amount of content you can play
• There’s tons of stuff to do in general and the writing, especially in quests, is charming and fun
• The in-game events are generally flavor events like Halloween, Christmas, and special game modes. There aren’t any “double XP weekends” or shit like that
• The only microtransaction is the membership bond, a token redeemable for two weeks of membership for those who don’t want to buy membership directly. You can buy bonds from the developer for $8, but you can also trade or buy them from another player using in-game money. This means you can technically “pay to win” by buying bonds and selling them for gold, but a high-level player can make gold more efficiently than that anyway so it’s a waste of time
• Players who have membership are elegible to vote in the content polls, where the developer proposes game content updates and only implements them if 70% of the voters approve. For example, the game is getting a new skill, Sailing—but only because adding a new skill was approved by members and then Sailing beat out the other choices in the subsequent round. The devs do still put through unpolled updates for “game integrity”, like bug/exploit fixes and necessary technical changes.
• Has easily the best wiki of any video game period, and an in-game “look this up in the wiki” button.

Cons:

• The developers (mostly when ordered to by their parent company) occasionally try to sneak enshittification into the game once or twice a year, till the players riot and threaten to cancel membership
• There is always some kind of drama going on, currently the drama is that a J-mod (one of the people on the Dev team) was temp banning every player who crossed a girl he wanted to impress
• The player base is pretty toxic by modern web 3.0 standards. However, as someone who’s played both games, it’s basically Daniel Tiger’s Neighborhood compared to the League of Legends community.
• Modern gamers might find much of the gameplay, especially skilling, to be grindy and monotonous. In other words, you might find it boring. There are ways to liven that up, but I also just enjoy a good grind sometimes too.
• It’s low-poly and ugly, though the players actually like it that way (and I do too)
• Addictive personalities might get REALLY addicted