Eh, I feel mixed about this. Gaming on iOS / Android (and any touch screen only surface -- especially with a screen 3.5" - 4" screen) can get kind of annoying. The main reason is that your fingers are blocking 1/3 to 1/2 of the display so that you can control your characters.
In my opinion, games like Madden, FIFA, Street Fighter, and generic platformers (e.g., Pix N' Love Rush) are much better when one has physical buttons and controls.
That said, yeah, gaming on mobile devices is going to be HUGE. But I don't think it's a drop-in replacement right now for anyone who's serious about gaming. Good for casual games and time wasting while waiting in line, but I don't think anyone has figured out how to truly nail it yet.
Yeah I'm still going to buy a 3DS.
That said with a PSP phone and Xbox Live on WP7, 2011 is shaping up to be the year cellphone gaming goes hardcore.
Portable standalone gaming is only dead when publishers of "serious" games (as opposed to casual games) decide it is, and move their entire game output to smartphones, and they don't seem inclined to do that any time soon.