The big advantage that Saints Row 2 has over the Third is the city itself. Stilwater is a great virtual city, with different neighbourhoods and many unique locations scattered about. It could compete with GTA IV's Liberty City. By comparison, Steelport was bland.
The game filled a gap that was left by the direction that GTA IV had taken. I don't believe that kind of gap is there today, however. I'd be fine with a SR3 style game, but the map definitely should be more interesting than Steelport. Plus optimization should and needs to better. While SR3 was a much better PC port than 2, it was not up to par by 2011 standards.
GTA4 (base) got very realistic, which I think was a lot of people's problem w/ that one. Personally, I loved it and appreciated it for what it was (still my favorite story and some of my characters are here in GTA4, pretty much) - but yeah, SR2 was an amped-up old-school GTA3/VC/SA kind of game, but I don't think it found its identity yet IMHO.
I think GTA4 with each DLC got less and less grounded. The Lost and The Damned had bikes and didn't feel as grounded and didn't feel as realistic as GTA4 base, meanwhile Ballad of Gay Tony took it back to the zaniness of older GTA's & had similar vibes (music, clubs, characters, locations) and whatnot that made it feel like an awesome modern-day GTA: Vice City.
GTA5 was great though. Overall, this is probably to me the best GTA game. With a really good story & lots of great characters (yeah, I love the main cast here - Michael reminds me of Tommy Vicetti, Franklin reminds me a lot of CJ from GTA: SA, and Trevor is just bat-crap crazy & all kinds of awesome & insane like a wreckless GTA-player would play the game).
Still, VC (Vice City) is my favorite GTA game. The 80's music & radio stations, the introduction of bikes, the setting of Vice City, so many Scarface references - yeah, I can't help but love this game. To me, it felt like GTA took what was great from GTA3, improved on it, performed better than previous version of GTA3, and went the artsy route (all the 80's). Not the best GTA to me, but my personal favorite. I loved GTA3, but VC was the one for me that always stuck out.