Like many others, my biggest complaints were the lack of proper vehicle deformation models and the almost complete absence of RAGE/Euphoria. The game felt like a major downgrade from GTA IV in these two categories. I disliked the arcade-like physics that the vehicles had at first, but I at least got used to them. However, even in a Patriot or Sandking XL, smashing into a vehicle at full speed does nothing. At best, you get some minor damage and if it's a good day, a fender might fall off. It feels like crashing a Futo into a dumpster. When the PS4 version came along, I hoped that they would improve damage, but instead they nerfed it even more by disabling roof deformation completely (at least by melee). I know it is to prevent your head from clipping through, but it's disappointing when you're taking your anger out on a vehicle and all you can do is scratch the roof and doors. Cars in general seem to handle like stiff 4-ton bumper cars.
As for physics, I hated that they took a major step back from GTA IV. Not that GTA IV's didn't have issues, such as stumbling for 10 seconds on a small drop. Instead of flailing around and utilizing self-preservation, they just drop like lifeless ragdolls. No grabbing onto ledges for dear life, no holding onto wounds, no shooting weapons out of enemies hands. It seems like injuries have been almost completely forgotten about in this rendition, and NPCs die almost absurdly easy at times, often by just walking into them or just with ONE punch. (That's another thing, the melee combat system is completely gone, and you can essentially kill anyone with your character's "super punch").
The story and humor of the game felt very forced at times, and the characters seemed shallow and one-dimensional. I couldn't really connect with any of them, and the game seems to portray them as narcissistic and self-entitled (I'm not sure if this was the intention or not). There are times when the protagonists go out of character solely for the sake of progressing the plot. A good example would be Michael, who has been in hiding and living his own life since 2003, all of a sudden decides to pull someone's house down from the hillside. Trevor felt like a "wacky uncle" character who was only there for comedic relief, and comes off more as an attention-seeker rather than a true criminal/sociopath. Franklin feels like a third wheel, like a pawn character who just ends up assisting in Michael's, and eventually Trevor's, dirty work. Hell, Franklin always seems so dead inside, as if he's just ready to be done with the mission so he can sit in his house all day or hang out at the bar. (You know, the only two things he ever does in his free time!) From the pre-release screens, as well as a new rendition of Grove St. and the fact that it is run by Ballas now, one may have assumed he would have had a role in gang-related missions, but that is not the case. Apart from Lamar and sometimes Trevor, the characters were completely bland and often came off as insufferable.
The city itself wasn't bad, but it lacked lots of details like trees, garbage, paper stands, etc. While there are some of these present, they are few-and-far-between. Cars and pedestrians aren't very frequent, and Vinewood Blvd. feels very empty and quiet. Props like destroyable fences and furniture don't break as fluidly, and the pieces just disappear after a few seconds. I know this stems down to technical limitations, but it makes the city feel empty and lifeless. Rockstar bit off way more than they could chew with the pre-release screenshots, and it was very disappointing to see a lot of the trees and props missing. Then again, thinking of how bad the lag would be with these re-enabled on last gen makes me cringe. The game already drops to ~20 fps in downtown Los Santos on X360. It sort of felt generic - there wasn't much graffiti and the textures seemed too clean. LA is supposed to have some trash and dilapidation. Another major issue with last gen was car spawning and de-spawning, which was pretty terrible. It was bad to the point that you could look away for a second and turn around, and any disabled vehicles would instantaneously disappear. I laughed out of frustration when I saw they would disappear in mid-air during a chain reaction explosion sometimes. A(nother) friendly reminder that we went a step back from IV.
Finally, Rockstar's approach on multiplayer and DLC. The multiplayer wasn't bad, but the constant notifications and overall "grindfest" of it all became very repetitive. Modders are pretty much expected on servers, and the only reason any action is ever taken against them is so Rockstar can keep selling their precious little Shark Cards™. I remember when Rockstar said they would never resort to microtransactions when GTA IV was out, and how they said we could expect single player DLC for GTA V. Now it seems as if Rockstar is taking a 180 on their philosophy. While in the end, Rockstar is a business, microtransactions only serve as a relief from grinding, and the whole concept can be considered niggardly at best. It seems as though single player has been completely forgotten about, completely overshadowed by GTA: Online. At least they used to throw the MP car packs and weapons into SP for free, but now SP doesn't get anything at all. I'll still probably follow the hype train for GTA VI, because I am a diehard GTA fan, but I hope that they see everything that went wrong with V, and put more focus into SP.