I'm at the point in the game where Trevor arrives in Los Santos, and I'm surprised how much I like the character. From the trailers and character description he seemed like a one-note psychopath, which he kinda is, but he's funny and strangely compelling. His introduction was incredible, especially if you played The Lost and Damned.
The cops: I hate what they have done with them, used to be you could get to a pay n spray or pick up a bribe star to get rid of em, and at least in 4 if you got out of the immediate area you could loose the heat, in 5 you have to loose line of sight with the police to get away and stay out of sight for a few minutes, difficult or impossible to do with certain (usually mission specific) vehicles
I like the change. The wanted system in the PS2-era games was a bit lame because you usually had to go to a pay-and-spray to clear it, I preferred the idea of GTA4's system but in practice it was too easy to escape. In GTA5 the cops are much more aggressive and it's harder to shake them. There are tips and tricks to deal with it, one of which is to get your car resprayed once you've broken line-of-sight, but there are other obscure ways of doing it such as hiding in a bush.
The Map: Scale-wise I'd say it's about half the size of San Andreas, and it's only Los Santos and the surrounding county.
It's actually around double the size of San Andreas' map. SA just seems bigger to you because of 1) nostalgia, 2) they crammed 3 (smaller) cities into the map, and 3) SA had such a terrible draw distance that it was impossible to get a sense of its true scale. This render from a map viewer
gives a good idea of how far away Mt Chiliad really was from the desert region, which was pretty much on the opposite side of the map.