I picked up the Mach 5 and the Racer X racer, plus the Pops/ninja assassin pack last night.
First up is a front shot of the vehicles with the figures in them so you can see how under-scaled the cars really are:

I have no idea why they didn't just bump the size up another 5% or so, or reduce the figures' sizes.
Two figures in one car. Racer X's vehicles is a little more roomy than Speed's, so it doesn't look
as out-of-scale. You get the idea that it's still not perfect though when you put two figures in at once.

Side shot with two figures:

Hidden features. These versions have pretty basic features (IE launchers). Pop out chainsaw blades or jacks would have been neat to see here.

Pops on the Battle Shell:

The ninja assassin is one of the better figures of the line. It's hard to go wrong with ninja figures though. He comes with a katana sword. No sheath or any other ninja gadgets. A mini motorcycle came in the Pops/ninja pack, so I guess you could give that to either one of them, as they both fit on it.

My favorite figure out of the ones I picked up is Racer X. I kind of like his car more than the Mach 5 too. Overall though, if you're not a big fan of the figures or vehicles, I'd suggest hunting for the reSaurus Speed Racer figures and Mach 5. That Mach 5 is hands-down the best one ever, and the figures are cartoon accurate...man, I miss reSaurus

Pluv already went over the articulation. I was surprised by the ball-socket joints in the hips and shoulders. Swivel biceps would have been nice. Seeing the articulation on these kind of makes me think this is the same style they're going to use on the upcoming DC mini figures. I bet they even use the same scale.