the characters do have depth

Some, but each is a massive disappointment:

• Trevor - most interesting IMO (esp. w/ end of game "mission"), but surely he's interested in ruling the Los Santos drug trade, so why don't we get any missions doing that?
• Franklin - most promising since he claimed to want to start his own business at the start, but once he gets money, he just chills at his house and doesn't do any more missions? The closest we get to ambition is trying to work with the Grove Street gang, but that's a handful of missions that go nowhere.
• Michael - the most developed, but also the least interesting; he's just a cuck whose wife is cheating on him and whose kids don't respect him, and his life's dream is to succeed at something he failed at years ago (massive mid-life crisis energy)

I guess there's a message there, but every other game had driven characters with clear goals that the player could relate with. In GTA V, the entire point of the game is just to get rich by doing heists, yet you only do five, and you can't even repeat them.

sort of succeeded in creating a game about nothing much as far as the themes are concerned

And that's probably my problem with it. Every other game had a point, which was steeped in satire at every turn. GTA V seemed simultaneously too serious (not nearly enough satire) and unfocused. Here are the previous games in the series (starting w/ III, I didn't play I or II):

1. GTA III - Claude gets shot by his GF during a heist, and is befriended by someone in a mafia family. Plot happens, he's passed between various criminal organizations, and eventually deals with all opposition. In the final scene, his new "gf" whines, and he's the one to shoot her, wrapping up his arc.
2. GTA VC - Tommy is released from prison and goes back to work for his boss. Plot happens, he sets up his own crime family, finds out his boss was the one to put him in prison, and he kills his former boss, wrapping up his arc.
3. GTA SA - CJ returns to Los Santos from Liberty City to find his childhood gang having lost most of its power. He helps them reestablish themselves, is betrayed, leaves Los Santos, and then returns later to reestablish the gang and deal with his betrayer, which ends his arc.
4. GTA IV - Niko arrives in Liberty City with a friend promising a new life, but is quickly dragged back into crime. He deals with various criminal orgs, and eventually either his best friend or girlfriend gets killed, after which he takes revenge. Having dealt with his problems, he finds out Roman's fiance is pregnant, implying he has new meaning to his life.
5. GTA V - Michael and Trevor fail at "the big heist," Michael thinks Trevor died, and both go on with their lives. Michael gets Franklin to help, Trevor arrives in Los Santos and finds Michael, and together they plan to have another crack at the big heist they failed. Plot happens, they succeed, and Franklin is given the choice to kill Michael, Trevor, or try to save them both. Michael's arc is largely completed, but Franklin and Trevor don't really get closure on their goals in life.

Each story was more complex and interesting than the past, but GTA V ended that trend.

Online component, which seems to be the second half of the story

Never tried it. Maybe that's why I dislike the game so much.

RDO

Also never played. I'm just not interested in any online component whatsoever, so I evaluate the games based on their SP experience.

Here is my list of Rockstar games that I've played by quality of story and character development:

1. RDR2
2. GTA IV
3. RDR1
4. GTA SA
5. Bully
6. GTA VC
7. most other rockstar games
8. GTA V
9. GTA III

I actually stopped and started GTA V a few times before deciding to force myself to finish it, because I kept coming back (people kept saying I should give it another shot) and re-downloading it just to be disappointed again was getting old. The game really fell flat for me, but at least I finished it and have no more desire to give it another shot. In fact, I played GTA IV after GTA V and had a much better experience (had started it on my Xbox, which died, so I re-purchased it on PC after playing GTA V). In fact, I thought Saints Row The Third had a better story than GTA V, and it's certainly nothing to write home about.

I hope GTA VI is better because I love the rest of the series, but there's no way I'm getting it anywhere near launch because I'm expecting it to be more like GTA V than previous entries.