For me the things that ruined the game was special abilities and GTA: Online.
Think about it, three special abilities, what are they? Slow-mo driving, slow-mo shooting and rage mode (+damage given, -damage received). This explains a couple things: car damage and overpowered cops/gang members. Have you tried getting in a gun fight with cops/gangs? you won't last long at all. The only way to have a chance is if you're in a car. Even then it's only a matter of time before you die. Cops will ram right up your ass, smash into you and shoot at you. Unless you buy armor/bullet proof tires then your car will just be a mess in no time. You don't want to be on foot when you're been chased by police as you most likely won't make it to another car in time.
Why are cars damaged so easily? SPECIAL ABILITIES. Oh, your car gets damaged too easily? Well, drive as Franklin and use his SA so you can avoid cops swerving into you or knock you off the road. That's what Rockstar want you to do.
Why are cops/gangs over powered? SPECIAL ABILITIES. Oh, you're getting shot at and despite having full health/armor are about to die after about 10 seconds? Well, as Michael or Trevor use their SA. Slow time down and head shot them f*ckers and get to a car and f*ck off. Or use rage mode to lower received damage and give you a better of chance of surviving a little longer.
Seriously, if cars were more durable and cops/gangs weren't so f*cking over powered then this game would be so much more fun. It's a sad day when you can't fight fellow criminals and get into a chase with police in a game called GRAND THEFT AUTO which is what this game is all about. They've essentially f*cked the god damn game up and ruined exactly what makes it fun.
As for GTA: Online. Well, that's an obvious one. Rockstar want to milk GTA for more money. Their focus has been on GTA: O. It sounds like a good idea but they're nerfing it so you have two options: pay them money to get more money in game or grind for hours and hours. No thanks. GTA V would be so much better if they hadn't bothered with GTA: O. Also, O has features than V doesn't have. Why? Why can't GTA V also have car insurance? It doesn't require and internet connection does it? just stick it as an option in LSC. The coding is all there. Cars are f*cking mess in GTA V. You get a sh*tty personal car which you can't get rid of which doesn't even sit in the f*cking garage at your house. Cars don't save if you put them in the garage. Oh but wait you have a second garage on the other side of the freaking map. Cause that makes sense. So you need to drive your car to the other garage to get a car you actually want. BUT BE CAREFUL!!! cause if you die or it explodes then you're f*cked. No way to get it back unless you hand over another $1,000,000 for that nice Adder. So, why can't GTA V have the same car system as Online? You simply get a car, buy insurance/tracker and no matter what happens you'll always have it.
There are other things in GTAO which should be in V but to be honest I can't be f*cked going on and on about it. Basically the reason GTA V is f*cked up is because Rockstar got greedy and they've ruined what made GTA games so much fun.