Years ago, I made an important decision: to stop playing MMOs. They had a tendency to eat up all my free time, interfere with real-life obligations, and generally stopped being fun long before I stopped playing them.
All well and good, and probably a story you've heard before.
A few months back, I noticed the exact same behavioral patterns when playing Path of Exile. It was eating up all my free time, interfering with real-life obligations, and had stopped being fun. But Path of Exile is not an MMO. While it is always online, and you can see other players in town, it's all instanced content, and can be played entirely without interaction with others. I had mentally filed the game under the ARPG category, not the MMO category; while I had put a lot of hours into Diablo 2, it was because the game was good. It didn't interfere with real-life obligations, and when I eventually got tired of it, I stopped playing.
What's the difference? Why do I react so differently to two very similar games? After thinking about it for a while, I think I've nailed it down: real-world timers. Path of Exile has two real-world timers: there are daily quests that can be run once per day (the masters), and there's the challenge leagues that run for a multi-month period. The daily quests create an incentive to log in every day, and the challenge leagues create a desire to finish challenges before the league ends. (And some of them require a serious time commitment.) These may seem minor, but to me they were the difference between playing a game for fun, and playing a game because I felt obligated to.
What does that have to do with games as a service? Because those types of games commonly feature real-world timers. Destiny 2 has daily and weekly quests. Middle-earth: Shadow of War has daily challenges. Overwatch has weekly events and seasonal events where you can earn seasonal loot boxes by playing. (Earning all the seasonal items requires a serious time commitment, and I have read some "familiar" stories.) Path of Exile is much closer to Destiny 2 than World of Warcraft in game structure. Games using the Games as a Service model want players playing them for months on end in order to create a market for microtransactions. One easy way to do so is to create an obligation to log in every day. This design is getting more common among triple-A games; I want to highlight this in order that people can make informed choices about the games they play.
(In the end, I decided not to completely stop playing Path of Exile, but I did make the decision to completely ignore the challenge system, and generally not get involved in the endgame. This means that the real-world timers no longer apply to the way I play the game. This ended up working for me.)
tldr: If you have a tendency to get "hooked" on MMOs, be cautious around any game with real-world timers, defined broadly. This includes daily login bonuses or quests, a season system, or timed events.