EDIT: misspelled 'become' in title. If a mod could fix that I would be very thankful
Sure there are a couple of new gimmicks every now and then, but in general, it seems like Blizzard just sticks to the same old formula time and time again. There is way too much predictability in their game design as of late, which in my opinion, makes the game feel stale and gives the game a shorter life than it otherwise would have. As players who have been around for a while and mastered the game, this predictability only compounds the problem. Even relatively newer players will pick up the formula very quickly, and it won't be long before they realise they start gaming the system, rather than playing the game.
Same 5 pieces of tier slots since Wrath
Same profession items every expansion (e.g. Darkmoon v18?)
Same materials collection
Item levels in multiples of 5
Instant catch up mechanics each patch
Same achievement patterns since Wrath (e.g. General, Dungeons, Loremaster, Glory, etc.)
Same reputation systems since Vanilla
Gear becoming even more streamlined
and the list goes on.
Collectively, they make the game feel too formulaic. Players have learned the developer patterns and behaviours and as a result, have become much more cyclical in their consumption of content. They know what's coming next (e.g. the catch up mechanics) so there's no reason to stay subscribed for this patch any longer. And it seems like the way that they are combating the problem is by adding emormous layers of RNG (e.g. +0-50ilvl? Titanforged gear) to the same stale old systems rather than shaking things up. I believe that this is the wrong way to go and will only cause more frustration, burnout and turnover from the playerbase than retention.
I believe that it's time WoW had a massive shake up at a fundamental level. The game's basic systems have become way too predictable even for relatively newer players and are well past their use by date. There needs to be a lot less predictability in developer behaviour with the content they produce and their systems.