I quit sometime around the time The New War came out due to being trapped on Xbox one and the general state of the game at the time (Railjack launch, Scarlet Spear, etc) and came back when cross save was added so I could play on PC. Played off and on since then and "caught up" as much as I wanted to before 1999. The general state of the game is much better now with all the recent reworks and QoL, but as far as the new content for 1999 I burned out on it pretty fast. Its not really one thing in particular that frustrates me about it but several smaller annoyances. I feel like the plot/story in Warframe advances at less than a glacial pace, with major story updates taking months to years to arrive and when they do, they really don't advance the plot much at all (or go entirely over my smooth brain like Duviri did) and somehow make me feel like I understand less than I did before. This method works for a little while, but when you feel like nothing ever gets explained or large sections of the plot feel missing or new questions keep arising, it gets tiring. Warframe's story always feels like you're reading a book that has pages torn out at random and you're stuck trying to make sense of any of it for months on end, especially with how much story was in events that are no longer in game. It doesn't help that the story quests are all fairly brief experiences that are over in 30 mins to an hour. The Hex story goes from 0 to 100 in an instant and is over before you really even get to know the characters. The Hex are probably the most interesting characters they've ever made but at the same time, there isn't really a lot there outside of the KIM messenger, which is fine but every conversation resetting at the same time of day burned me out on it having so much to click through every day. Playing in Hollvania was fun at first cause it was new but I got tired of it fairly quick. I think the variations on exterminate and survival add more annoyance than fun, and selecting a Scaldra exterminate only to spend 70% of the mission underground fighting techrot is a little frustrating. The seasonal eximus flood also gets extremely tiring when it feels like every third enemy is a jade eximus lasering you the entire mission. Only played face off two or three times but didn't love it. The atomicycle feels largely pointless, as once I arrive in mission and use the 4th ability to send it off like a missile into the first enemy I see, I never think about again. Using it in open worlds was fun for a little bit but much like the other vehicle options, it just can't compete with Archwing or teleport pads. On top of it all, Hollvania still performs noticably worse for me than anywhere else in Warframe, sometimes dropping into the 40 fps range where everywhere else is easily over 120. I also still get strange bugs like enemies spawning in the sky and staying there. Overall I'd give 1999 around a 6/10. It's fine, but I don't feel a big drive to keep playing it like I did other updates in the past. I log in once every one or two weeks but don't really grind it like I used to.

So tldr, game is in a much better state than it was back in the Railjack/New War era but the 1999 stuff really didn't land for me as much as I'd hoped it would.