I expect a lot of underwhelmed people once E3 hits, as the hardware appears nowhere near as powerful as they hoped/hyped. This will be due to a vast majority of third party support being composed of ports, which look near if not identical to their 360/PS3 counterparts. I also expect some of Nintendo's own work to fail to deliver on the hardware's true capabilities: I don't expect NSMB Mii to look impressive at all, and I wouldn't be surprised if Pikmin 3 looked curiously like a high resolution Wii game with polished up assets and shaders bolted on.
I predict most of the controller gimmicks will be forgettable, especially from third parties. Most games will simply use the pad for item selection, and maybe for goofy puzzle integration. Nintendo will show some cool ideas, but they wont be in launch titles. Despite backwards compatibility, almost no game will be shown using the Wii Remote + Nunchuck. This will depress me.
Online will be improved over the 3DS, quite noticeably, and I expect/hope there will be a few pleasing surprises. But it will still have plenty of dumb shit because Nintendo's track record with online is severely questionable. That and I loath the eShop.
In all I expect E3 2012 to be pretty typically Nintendo. Those who love Nintendo will have lots of cool shit to look forward to, some of it looking amazing, others not so much. Third parties will impress Nintendo only gamers with a plethora of welcome ports, but multi platform gamers won't care all that much. Those disinterested in Nintendo titles will see nothing of value with the Wii U, and will continue to ignore it, and let everybody know they're ignoring it.