Like with the PSP I predict it will annihilate the Nintendo offering. Maybe this time it'll work.
Software is kinda twofold for me so far. It looks like they really don't have all that many games so far, but from what they have shown some are reasonably interesting to me, enough to buy in at launch. Never played MH3p, only MHTri, so that alone would probably keep me busy.
Hardware is, for lack of a better word, porn. Price, existence and extent of regional locks as well as battery life will be the defining issues with this. I want the 3G version (I'm sure they'll split into 3G&WLAN and WLAN only), and that shit's gonna be expensive.
Really hope they improve the UI some more (or allow extensive reskinning). Still, it looks like it'll work, so whatevs. I lived through a horrible UI with the PS1, I will survive again. I'm a trooper like that.
For those with short memory, it looked like this:
spoiler (click to show/hide)
[youtube=560,345]
[/youtube]

And that name...

Jeez.