Think about it.
This gen brought us a huge focus on HD. Many people purchased HD TV's for the first time, and wanted a system that could play in HD.
This gen also brought us an extremely rare "fad" known as the Nintendo Wii that was comparable to the Tickle Me Elmo craze. I highly doubt any of the 3 manufacturers strike gold like that any time soon.
It's also the first real gen where Online Gaming really took off across all the platforms. I expect an improvement from Nintendo next gen, but for the most part, Online has been maxed out on it's potential. The entire Fighting genre was re-born on consoles with large thanks to online play. SFIV and MK would only be fun for 10 minutes if it werent for online. It also made games like CoD mega popular due to the multiplayer aspect. But it's getting old at this point and there is a lack of variety in online games now.
I just don't see room for much growth next gen. Nothing "new" to entice gamers. 3D had potential but I just don't see it taking off the way HDTV's did.
Next Gen will see the smallest improvement of any generation leap, and lower sales than the current gen.
