At a recent multiplayer event in San Francisco, I was able to sample all three components of Party Mode: Invasion, Outbreak and Transporter. And no, Jason Statham is not anywhere to be seen in that last game type. (It's better that you're disappointed now than when you pick up the game in May.)
The game type most resembling my childhood "sibling battle mode" in Wave Race 64 was Outbreak. All cars start in a ring formation, in the center of a large, Gymkhana-like obstacle course, and await the conclusion of a five-second countdown. Once it reaches zero, the "infected" vehicle is chosen and the other cars must avoid it in a frantic game of tag, before they're all bumped and infected within the time limit. The last remaining healthy car gets the stash of points.
Both maps I played were on concrete surfaces, using a variety of 4WD cars, like a WRX, a Lancer EVO and a Ford Fiesta. But the cars didn't behave like I would expect them to on asphalt: they slid around like crazy; they barely had any grip; and I found it extremely difficult to navigate the platforms and ramps in each stage.
This general chaos extended to the other two, less interesting modes, as well. Invasion, a mode where big cut-outs of skyscrapers and robots are periodically spawned into the level as a chicane of sorts, also suffered because of the handling. Precision steering is crucial, since hitting a skyscraper will deduct a point from your score (while taking out a robot will add a point).
Transporter, finally, is a Capture the Flag variant where players can steal the flag from an opposing player by bumping into them. Having to drive up ramps and reach odd spots of the map was difficult enough without speeding cars barreling into each other, but that wasn't my main issue with this mode. It fell flat due to each round devolving into a clash of bumper cars -- without fail, a group of four cars or so would become tangled so deeply each round, all I had to do was stay away. When it looked like the flag bearer was going to make it out of the pile, I could simply swoop in, bump him, and make for the flag drop-off. Of course, I spent my fair share of time in the pile prior to developing that strategy, which was an exercise in frustration, to say the least.
Outbreak is the obvious stand-out here, offering a different experience every time. It was fun sitting in a room with other journalists, gloating when I dodged that near-collision with an infected car, or complaining when an infected car came from my blind spot and nailed me. It was a mode full of tension, surprise and competition, and was the only game that still embodied the qualities I value in the rally racing.