The coolest feature so far is the upgraded RAGE Graphics Engine (also used to power Table Tennis), which finally replaces Renderware under the GTA hood. RAGE now features a heavily customized version of Natural Motion's "Euphoria" physics engine, which got major attention last year when LucasArts demo'ed it as part of the Indiana Jones and Star Wars games. Expect even more excitement as you see how the teaming of RAGE and Euphoria affects movement, gunplay, climbing, and driving. Rockstar also points out that everything you see in the GTA IV trailers is capture in-game -- there are no underhanded renders here.
While the Natural Motion has a visible effect on the physical aspects of action and gunplay, even more noticeable is the game's audio system. Positional audio makes for the sort of intense, fun gun battles we've always wanted in GTA. The streets sound -- and feel -- real.
Part and parcel of the audio system, of course, is Rockstar's trend-setting ability to craft a killer soundtrack. The new trailer is scored with "Arm In Arm (Shy Child Remix)" by New York City-based band The Boggs. The idea was to show a real street-level view of Rockstar's version of the city with a band that belongs there. To that effect, you'll be seeing even more licensed music from all genres and time periods, since the soundtrack team is no longer confined to a specific decade.
While Rockstar is reluctant to discuss the details, time is a big factor in GTA IV. The new trailer indicates in subtle ways how the passage of time might affect the game, and there are clues that indicate some missions, or mission elements, might be time-specific. And if that's the case, then can multiple outcomes and branching storylines be far behind? Don't expect a mission flowchart that looks like a New York City subway map, but Rockstar could surprise us.
5. The Details
The vastly upgraded graphics don't just make for a shinier front end. Rockstar has worked to make GTA IV follow through, from the biggest details to the smallest. You can see it in the way Niko leans around a corner, or how he sways while hanging (in real-time, procedural motion) from the skid of a helicopter. It's the glance into a car and the ways in which the streets of Liberty City are teeming with the life we've been waiting to see from the series. Rockstar claims the new graphics, sound, and details make the game more beautiful, not more disturbing, and we're almost ready to believe them.