R* nailed the weapon sounds perfectly in RDR, but in every GTA game they have just sounded horrendous. The assault rifles sound like rapid-fire staplers. On the same note, the sound of melee weapons was similarly unconvincing, the knife/sword and bat being the worst offenders.
That said, I'm greatly anticipating this game, especially after the quality of the soundtrack and other effects in RDR.
I hope people don't flame me for saying this, but DICE do a great job with their weapon sound effects. I think DICE have been known to assist other dev teams in the past, perhaps they could chip in here too.
As much as I love GTA, it does have some goofy gun noises. Their not awful, I've heard much worse but some of them just sound off. The M4 and the SMGs sound fine but the AK-47 for example has a very distinct sound. One of those guns that even if you've never heard one, you could pick it out of a group of other assault rifle sounds.