Stuff that wasn't in the trailer that is confirmed:
Looting, co-op heists, deathmatches, races, gang attacks, crew vs crew playlists, sports (like tennis, BASE jumping, golf and more), plus 'ambient' events like armoured van robberies, crate drops, import/export car acquisition, bounties
When you speak into the microphone, your characters lips will move in-game
You can select what masks you use to hold up places like gas-stations and banks. You can then throw the mask away which will remove a wanted star
During heists, if you speak loudly into your mic, the AI reacts to the urgency in your voice and puts the money into bags quicker
Whoever does the job gets the cash and can choose how much to share: a sure-fire source of arguments
Police cars have a 'cone of detection' visible on the radar and you need to stay out of their sight for a number of seconds - or simply out-distance them - to lose the wanted level.
Like single player, car modding is extensive, but don't fear losing your cherished vehicles. You can take out insurance and ring for a replacement car if yours get destroyed. Your custom cars show as markers on the map and get impounded if you leave them too long. Simply pay to retrieve them
The garage looks like a minimalist, gleaming white Apple showroom. You can pay a personal mechanic to fix your cars automatically, or deliver them to any location.
At one stage, a car flies past us at a junction being pursued by the police - another human player in trouble, since you exist in the same world
If this wasn't enough, Rockstar will constantly add missions and content to GTA Online, plus players can create their own missions using the Creator tools. The long-term aim, as we understand it, is a vibrant self-sustaining community, but initially the tools will be more limited - like the mission creator in Infamous 2. You'll only be able to make races and death matches at the start, but multi-stage DIY heists should appear at some stage.
You can assemble a team from your friends list, or recruit according to specialist skills. For example, some players are better at shooting, driving or flying, while others have access to unique vehicles.
As GTA Online develops, it's sensible to expect the 'Whales' to rise to the top - players with more time and skill with the highest levels of RP and cash. However, it's possible to spread the wealth by sharing cash, weapons and ammo among your team. In turn, they can 'defect' and try to steal your cash so, like life, GTA Online is an exercise in trust and social dynamics.
Before the demo's final mission, one player leaves to drop money off at the Maze Bank ATM. If you get killed holding all your cash, a portion will spill onto the streets. It's important to keep cash for your daily activities, and deposit the rest in the bank. Or wager it on races. Or invest in the stock market
You can even attack listed companies and damage their share price. At one extreme, you might need a bodyguard to make drops at the bank.
There will be loads of property to buy at different prices, according to their views and location. You can use your in-house CCTV to spy on people at your front door, or take showers, surf the net, change clothes and watch the game's many TV channels. From the safety of your house, you can watch people within your 16-player game being chased by the cops, just like Police Camera Action.
Leslie Benzies claims that Los Santos is only the beginning. The volume of creator tools, missions and items will grow, but at some stage GTA Online will head into new locations. He suggested they were sitting on a lot of content, and it doesn't take a genius to speculate what it might be. Fancy taking your Los Santos crew for an away day in Liberty City? What about a retro-themed GTA Online spin-off in Vice City, but with deliberately old-school graphics like Far Cry: Blood Dragon? Leslie Benzies confirmed nothing, but suggested that old content was on route... simulating the world and different countries has always been their long-term goal.