My example: There's one game mechanic that ruined Gran Turismo for me from the 5th game onwards: Prize Cars for complezing Licences.
I loved how in earlier GTs, you started with one car and it took ages before you saved enough money to even think of buying a 400 HP car and doing the high-level races... Now I don't have to worry about that, because my garage is full of Ferraris and Lamborghinis even before I finish a single race. And to balance this, they added a LOT of car-specific races, where they FORCE YOU to buy a specific car, where in earlier installments, you had to think long and hard about which car will you purchase to allow you to compete in different tournaments etc. Totally ruined it for me.
Of course I can just sell all the prize cars, then buy new ones, then sell them again etc. until I have about the same money as in the beginning, but that takes a long time and it sucks, as you can't get some cars any other way.
Also, the special events where you don't need any car of your own that give you even more high-powered prize cars for almost no effort.