It's hard to really pinpoint one, because aside from the consoles themselves, they're all intertwined in some way, when I look at the things I like about this generation, which comes down to immersion and storytelling mainly.
- Awesome graphics and physics (and sound if I might add). These have really done a huge trick for storytelling and immersion for me. Some examples would be Uncharted 2 (seemless integration between cinematics and gameplay, and the amazing animations and levels of detail that help bring characters and environments to life), Killzone 2 (amazing atmosphere. I don't remember what it was specifically, but some moments in the game just felt more compelling and 'real' (not realism, but in the sense that I was there) than anything I have played to date) and Flower (just go play the game).
- Motion controls. This one isn't as big as the last one, and it certainly isn't at a point where I am satisfied yet, but playing Wii Sports Resort for the first time and seeing some of the things the M+ did was amazing. And playing Heavy Rain, I found that even small motions can make a big difference in immersion. I'm not an avid Wii player, but I'm sure I could name more games that are enhanced by motion controls if I did, but right now, I can still name many games that use Sixaxis and are better for it.
- The games. This is probably the biggest one, because even though the hardware has limits, designing your game right is where it's at. And fortunately game design has moved forward too, just like the hardware and the limits set by it. Games like Heavy Rain and LittleBigPlanet are throwbacks to genres that have been visited time and time again since the early days of gaming, but they bring new ideas, designs and implementations that make them outstanding and fantastic games in their own right. And even games like those can be a gamble, but you also see games like Flower and Prince of Persia that take new directions in game design, and both are great games in my opinion.
- The innovations. This one is hard to say a lot about without being, as most things people consider to be 'innovations' this generation are merely an evolution of older products. So let's just call it "The stuff that is normal in this generation, but we have seen something off before". I think downloadable content, online multiplayer on consoles, achievements/trophies and motion controls have all enhanced our gaming experiences this generation (though not all implementations have been good).
So there you have it, I'm not voting for a single one of those 