The graphics in that trailer are absolutely mind-blowing, and I have no doubt they will be scaled down significantly for the consoles. Doesn't matter. I never got much into GTA4, but I have been consumed by the Red Dead Redemption GOTY edition I picked up not too long ago. Playing poker with other real life squarejaws in an epic downpour, talking shit and having a good time, is really a special video game moment. I love the relaxed pace you can take the game at, and much appreciate the added difficulty in Hardcore mode. You have to be way more tactical when approaching mobs now.
So my thinking is Rockstar manages to take what they learned from RDR, mix it up with what is obviously the single most fertile GTA setting possible (yeah, LA has gotten played out in video games lately, but consider the social commentary Rockstar prides itself in in these games, and look at what has happened to the greatest state in the Union since the economic collapse - a theme played up in the trailer - and it's going to be nothing less than monumental), and spit out the single best game of the console generation.
A couple of things I really want to see:
the ability to rollerblade
bring back working out. Getting swoll in the gym in San Andreas was fantastic fun (as was getting Heavy D obese and riding a bicycle). Also, martial arts.
An epic Hollywood sub-plot
Scientologists
Drug Cartels
Co-op bank robberies
And I am willing to lay money on there being multiple playable characters, and those characters being Tommy Vercetti and CJ. Bet.