It's definitely a 7 for me. I was really excited to get away from the concrete jungle vibe in LC when it first released, but these days I just keep on coming back to IV due to the lack of it tbh. Los Santos, while actually larger than IV's LC and Alderney in technicality, felt smaller due to the open design of things. I know real life LA is full of massive open streets and such, but look at San Andreas' version of Los Santos. It was a fairly small map in general, but it felt bigger thanks to the layout and road mapping (draw distance also played a massive role but making V have small draw distance would just be weird). GTA V's LS just seems like it was built with a racing game focus in mind, yet there are barely any street races, and almost none of them make use of downtown's huge open streets. Los Santos also had very weak vegetation compared to real life LA (but that's for another rant).
Once you move out of LS, the roads start to get a lot more complex due to the mountainous landscape. Liberty City had a huge grid like map and a bunch of water that made moving to the next island at least a tad bit inconvenient, giving the illusion of size. Los Santos has a bunch of mountains that just seem like bad excuses to make annoying winding roads that drag on your journey. I know that real life LA is actually pretty much surrounded by mountains, but I feel like they could have let creative geography take charge here instead of realism. They could have just left Mount Josiah and Chilliad stay, while trading in the other ones for more exciting, unique small communities. San Andreas had a good bunch of small towns to explore and they really made the countryside a lot more fun (imo).
Once you get past the first few layers of mountain, you come across the Grand Senora Desert. In reality, it's not really grand at all. It's a Vice Beach sized stretch of sand textures and fences. They could have at least removed those hills next to the Liqour Ace to make way for more desert land. Real life Slab City has massive open stretches of desert and a few main roads going through it. To the west of it is Raton Canyon, probably the only area I little problems with.
The last layer of the map is Paleto Bay and Mount Chilliad. Paleto Bay should've had much, much more forest area than it does. It's not a dark, desolate forest, untouched by man. It looks like a park with big trees and a highway going through it. It's a nice area, sure, but it could have been something bigger than 3 straight lines. Unlike San Andreas, Mount Chilliad doesn't have any proper roads going up it (probably more realistic that way too). Instead it has two tight hiker trails. Most of the time when you go up it, you use aircraft or take one of the trails. One starts out in Paleto Forest and the other in Grapeseed, so you only ever see two sides of the mountain. They could have added more trails that go up it near the Up-N-Atom rocket joint in Paleto or by Stab City, so you get to see more of it. I like the fact that they placed a (letter scrap?) collectible on one of the cooler flat arch areas (no idea what you call them) on the mountain. Sadly, doing 100% is probably one of the only times you get to see such nice areas. Whether that's a good or bad thing, I'll leave for you to decide.
In my opinion, they didn't do a very good job of utilizing the whole map. The east side of the map feels very neglected, which is interesting because Mount Gordo and the forest area behind the oil fields (at least in my opinion) were very well built. You spend most of the story and even side missions sitting in Los Santos or going up and down Route 68 like a paraplegic in a rocket wheelchair. Even with all of my rantings about "what could've been" and how the layout sucks donckey dick, it's the small things that really bring it together. The bumps in the road with actual depth, realistic cityscape, unique pit stops like Rebel Radio or the pink dino near the quarry, background sounds, animals, animated oil wells, traffic cars (not counting all the sh*t from latest online updates), "random" events and few copy pasted assets. It's better than previous maps, but it could have been better than it is right now.