I play Pokemon as a case study at this point because Generation 6, 7 and 8 were just literally not entertaining to play. I'll give you a brief rundown:
>Games are getting progressively easier, on-rails and very main story centric
>Competitive mechanics haven't evolved much since gen 3, and it's still a massive drag to play it competitively in-game; the battles are mega slow and really demanding time-wise to create a team. Plus the reward is pretty bad anyway, it's not a truly competitive game, it's filled with game deciding RNG.
>Actually challenging in-game battles haven't been a thing since Emerald's Battle Frontier
>There is a huge creativity barrier by now because almost every type combination and logical stat distribution has been done
>The bloating of Pokemon makes the whole "catch 'em all" aspect really terrible
>Technology-wise it's absolutely terrible because it's been restricted to weak handheld devices, and Sword/Shield a complete hack job
>Online is great, but as you'd expect from Nintendo it's a cumbersome mess to get going, and it also really trivializes a lot of the rarity factor of Pokemon - you can breed almost any Pokemon and trade countless eggs online, people hack things left and right, etc
It's honestly in a very low point, and it shows a crucial weakness of the series: it's designed for kids. But not only in the literal sense, but more in the cyclical sense: it's designed to impress a new generation of children who grow up by the time the next game comes around, rinse and repeat. Basically every generation gets roughly the same experience from these games, but playing more than one generation is not very satisfying.
The series just never really evolved in the logical direction it should have (open world, free roaming, exploration focus) but ironically took the opposite direction. The constant bloating of Pokemon also really devalued a lot of the mystique about it, it's kinda grotesque by now when you have like fifty "legendaries".