Did you like GTAV's ending? It kinda felt rushed to me, like maybe they were running out of time or budget and had to find a quick way to wrap it all up. It's been a long time since I've played it, though, so I don't remember specifics.
The story is definitely the weakest aspect of GTAV. To me it seemed like it lacked a narrative thread for most of the game, focusing more on cool scenarios like the heists rather than concerning itself with telling a coherent story. You do get some stellar mission design as a result of that, but in the last few missions it's like the game suddenly remembers it has to actually do something with this trio of characters.
Another problem was the weak villains, which again the game doesn't do much with. The trio do so much shit to Madrazo like ruin his home and kidnap his wife. R* then use that as an excuse for more heists so the trio can pay back Madrazo, which of course is a fun diversion and all, but the payment from those jobs just totally defuses the situation. Madrazo, a man powerful enough to exile you from Los Santos, just slopes off like a coward, never to be seen again. It could've been more interesting if he'd played a bigger role as a big bad who comes back later on, perhaps replacing the role of Cheng and Stretch (who just seem to come out of nowhere as antagonists). At least there would be a more personal beef with Madrazo. The other antagonists like Devin Weston and the FIB guy just were't very memorable or even particularly evil - just opportunistic, narcissistic dudebros who are more annoying than anything. In another GTA game these would just be any other mission giver, not the main event (like a Brucie in GTA4).
My final issue with the story is the ending dilemma of who Franklin has to kill. It seemed to me like Rockstar were trying to do another clever ending scenario like they did with Red Dead Revolver. However, giving the player the option to not kill
either Michael or Trevor, and just go kill the FIB douchebags instead, completely deflates the weight of the choice. NOBODY ON THIS GREEN EARTH is going to permanently kill off an interesting main character, for an under-developed plot reason, when the choice of saving both exists. Why even bother giving the player that choice at all?
Sonny Forelli in VC, Tenpenny in SA and Dimitri in GTA4 were all much better developed villains and those games had a more compelling escalation of the story events. Even just the way they'd phone you throughout the game to taunt you built them up as someone to be hated. You actually got a sense of closure and finality in all those games, which you don't in GTAV, where it's more of a "that's it?" feeling.