First impressions:
REALISTIC DRIVING PHYSICS SUCK!
Seriously, it's not that bad, but it takes some getting used to. You definitely have to choose your vehicles much more carefully and mastering the gas/handbrake combo to power slide the corners is a must.
No more getting fat, hungry or tired. Hurray!
No more load times going in and out of buildings. Double hurray!!
The melee fighting options are a much welcomed improvement. You also have the option to spare or kill certain NPCs for different after effects. Basically, you get to decide how far you want to take things. ♪ Kick, punch, it's all in the mind! ♫
First time I crashed head first into a guard rail and flew out the windshield (and over a cliff into freeway traffic) I laughed my ___ off.
The new cell phone is not as annoying as I had feared it might be and is actually really handy.
The multiplayer is fun, and I usually hate online multiplayer. Cars, guns, innocent bystanders, huge areas, lots of game options besides the usual boring deathmatching (and I have to admit that even the DM is kinda fun.)
Spending time socializing with NPCs earns favors from them, like having your cousin send free taxis anytime/anywhere you call. Never thought I'd enjoy taking a date bowling, especially in a GTA game. :lol Darts is way too easy, though.
Lots of little touches of realism, like watching motorists toss litter out the windows or getting your hat knocked off.
Very few power ups. I'm not sure if they're just well hidden or what but I have yet to find a single weapon or body armor pick-up (in single player) and very few health ones. Fortunately there are hot dog stands and restaurants everywhere to heal, but saving at the safe house doesn't restore HP. WTH?
Also, not a lot of money lying around. You can even kill a vendor and get nothing. Double WTH?
When I finally found a gun shop there was only one gun available at first, the other dozen were locked. "Check back later!" I can't even find a hardware store, so the only weapons I have so far have been earned in missions.
So far, no properties to buy. Maybe that'll come later as more missions open things up.
Overall, they seem to be striving for more realism, but there are some odd, illogical moments. Like when I was taking my date home and got into a police chase. She was woo-hooing and having fun one moment, then a few seconds later says, "No offense, but I'm getting really bored. Please take me home." Huh?
I'm still very early in the game, though, and there's a lot going on here, so this is far from being a final judgement. Looking forward to much, much more to come.