I downloaded the HD version from Rockstar.com and watched it over, and over on a 42 Widescreen High Def TV. I also haven't read any of the other breakdowns so I could do this for fun.
The city is different and has some landmarks. At 0:39 behind the construction you can see the famous U.S. Bank Tower.
Blimps: 0:17 look at the sky to the right for the first evidence (Golfcarts are back). Take a look at 1:03 of the trailer and you will see a blimp in the distance, also under the G at 1:24.
At 0:58 there is a homeless guy with a cardboard that reads "NEED MONEY FOR BEER ****, **** (AT LEAST I'M NOT BULL*******)"
Clubs and motorbikes make a return. At 1:02 you will see some guy being thrown out of one, and a bike.
0:07 Dog, and seagull.
Jet Ski at 0:19.
0:37 the narrator says that he is a dad. Looks like we have kids, but what about a wife?
HUGE mountain at 0:22 suggests out of city enviros.
At 0:24 a new feature is seen. You can now put the roof of your convertible down while driving 8)
0:32 we see Los Puerta Fwy, and Downtown Little Seoul on a Highway sign. Could we see a return of Wu Ze Mu? And Fwy suggests travel between two cities. San Ferro would be my bet.
0:33 there is an exercise yard called muscle sands. GTASA had places you could go to build up the main character CJ, could this make a return?
There are four planes 0:43 is a poison gas crop duster. The narrator says "you know how it is" as four Mexicans get gassed, could this mean that the main character is Mexican? Also to support this is a Mexican looking guy with an AK47 at 0:47.
At 0:47 the guy with the AK47 has it modified with a silencer, could this mean we can now mod our guns!? - Also at this time is an R* joke; the van has a pest control phone number on the back that says 1-999-BUGSTAR :P
At 1:00 we see a guy in clothing that would cost a lot of money living under a bridge. Sadly because of the economy today, a lot of businesses have gone bankrupt, this would suggest that this game is set today in pre-depression USA (In reality I hope not).
After the guy under the bridge is a fighter jet.
At 1:07 you can see a building that was in the original GTASA! It was the home of a massive shootout in that game :!:
Above the VINEWOOD Sign is a 747 jumbo jet.
1:11 is a private jet.
I'm still looking and will update HERE (as will others)