I'd give it a Solid 8! I still have like 100 side missions to do, but I think I'm done.
I just finished it last night as well and can't decide either if I want to do all that side stuff or not. There's just so much. I only have 3 more peeping tom things to do I believe so I might finish those at least and I've only done 1 of the AR games so far so I'll probably try those other ones. Can't believe I haven't done the spider robot yet, heh.
Maybe I'll do a couple more gang hideouts too, those were pretty fun.