School system: One of the downfalls of a game that has an open "beta" (or whatever you want to call DoL's current status) for many years is that players will obviously experience what already exists the most. Someone who's put a thousand hours into the game will naturally find certain things a lot more annoying and tired than brand new players...such as the school system. This isn't strictly the fault of the content in question nor its general level of quality or implementation, it's just a natural function of having put too many hours into one game, learning all there is to know, and having done it all so many times that it's become rote and stale. Over-consuming something, even something you originally found great, has a tendency of ruining whatever that is for you, which is why I generally recommend people try taking breaks from hobbies when it seems clear and obvious that they need one. Though I guess some people are able to watch shit like The Office a gazillion times and never ever get tired of it no matter what, so maybe this rule is more or less applicable to certain people. Anyways, point is, if the development cycle of your game is going to be five or more years long, it's going to be very tough to always be on top of certain content getting 'old' for your most loyal playerbase, and I'm not exactly sure what you can do about it outside of frequently adding on to or re-doing work you've already done.
Difficulty: I'm in favor of the game getting more difficult generally speaking, though at times I find the monthly payment to Bailey a bit burdensome once its reached its max of 4000. It's not that it's impossible to make that by any means, but rather that it starts funnelling you into certain ways of playing that maybe the player would rather ideally not go down (or at least stick with) if they didn't have to. When something becomes too difficult, it often becomes a game of "what works is not very fun, and what's fun sadly doesn't work". Once you've reached that maximum monthly payment, the player necessarily becomes more constricted and loses a bit of their agency to be able to interact with what they wish to interact with - unless they find a way to break the money system entirely, of course. But some level of challenge is good, so becoming a bazillionaire is not ideal either. It's a tough balance to perfectly strike: I want to struggle, but not so much that I feel like I can't afford the time to do random jobs while wandering the streets between all the different things I'm already supposed to be doing, you know? I don't think there's necessarily any fix for this, pretty much all singleplayer games with some kind of money system are exploited and broken by the player sooner or later, and I don't see DoL being able to magically fix that age-old problem.