I'd give it an 8. Gameplay is a major improvement over IV and seems to continue the trend set in the excellent BOGT. That said I feel like the story and emersion were weaker than in IV. I could relate to Niko a lot more than the character's here and for me with the exception of that game's ending and few rushed parts in middle that game had a solid and compelling story IMHO. At times when playing V I have to admit that it sort of felt like Saint's Row (I don't mean that as a compliment). Trying to hard with it's humor and just a little too over the top. I dislike Blackwater as much as the next guy and having a stand in for them was a good villain but at the same time it didn't really feel super GTA to me... just a little too much crazy sh*t.
The thing that for me will always make San Andreas an awesomely epic game is that whether or not the story was brilliant or dialogue well written it had an almost Star Wars like mythic quality to it. You come in after being away from years, have to get to know everything again and when things are finally looking up there's this massive betrayal and you have to flee and hide. You start new in a new city and things are going good but there's still the unresolved past gnawing at you. So you strike a major blow to your enemies, work with some shady government types, make new friends and open a casino, work with the mob, rob a casino and after all of that it is finally time to go home and make things right. You take back Mad Dogg's mansion, take back the Grove, Sweet gets out, you help Cesar, you track down OG Loc and you finally take out Smoke and Tenpenny... the whole last chapter is this awesome revenge fueled victory. I don't think IV got this and I think V fell even further from this. Somehow BOGT felt the closest to me but it was such a snippet. I think it may be because at the end Bulgarin and the Ancelottis felt like absolute scum that you hated and wanted to take out at all means possible. Weston, Pegorino, even Rascolov didn't have what Bulgarin or Tenpenny did. Haines for me was a bit more hateable but even he paled next to someone like Tenpenny. Weston had every potential but he was too much of a buffoon... I mean the last mission (assuming you choose a the right path) is a complete joke; he's too easy.