I’ve been playing since 1 as well. 5 completely killed any desire I had for the series. There’s some good things in it, it’s not a bad game or anything. Definitely something off though, I agree.
It was the overall downgrade from 4 that stood out to me. In 5, guns sounded worse, the driving became way too arcadey, the story was less tight and the three protagonists were more disjointed and Franklin was grossly underdeveloped, the city lacked diners etc to go eat at etc and felt less alive, no vigilante missions, NPCs were squishier residual in hand to hand, the car damage models are boring and less detailed than 4… I could go on.
5 was bizarrely a huge step back from everything they’d built towards for 4 that it’s no surprise 4 has remained hugely popular and maintained an incredibly active modding scene to keep the game looking youthful.