Those changed your mind? Aside from Donkey Kong, we already knew those games were coming. What about Mario 3D World or X blew your expectations away that made you want to purchase a WiiU?
Well, we didn't know or expect that Mario 3D World was coming out. I was expecting something more along the line of 64/Sunshine/G1/G2. But when I first saw the first seconds of the Super Mario 3D World footage, I immediately thought it was a Super Mario 3D Land sequel for the 3DS. I've been playing, and replaying Super Mario 3D Land for months and months now. The more compact levels make replayability easier, at least for me. In contrast, I played through Galaxy 1 and 2 once each and haven't touched them since. That's one reason why the WiiU is on my "to buy" list now, instead of waiting for ZeldaU. Had they revealed "Mario Galaxy 3" I probably wouldn't have changed my mind.
While they didn't release very much new information about Monolith Soft's new game "X", if you compare the last trailer they showed for it, back in January, to the new trailer at E3, it sure looks to me like they've made huge strides in game development. Maybe it was just the quality of the video I watched back then (although considering the 6 month difference I bet it has more to do with development), but while the first trailer did look big and interesting, the new one... wow... just wow! The old one is... "blurrier"?... and "chunkier"?... and generally looked like something they could have pulled off on the Wii (MH3 and Xenoblade Chronicles for example). This new trailer does not look like a last gen game. Much smoother, and with better lighting and models and smoother animations. Personally, I'm sold!
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What about XY/DreamTeam/Sonic was shown that convinced you to purchase those games and why weren't you considering it before E3?
Well obviously XY were on my "to buy" list. They did release a crap ton of information on it though. But Sonic and and Dream Team definitely weren't.
I'm not a huge fan of sonic games. They're alright, but I'm not a giant fan of sidescrollers, and they've pretty much screwed up all their 3D outings so far (arguably). But watching the new trailers they released for the 3DS version, I'm really getting into it. I can tell that the very distant backgrounds and the long, stretched out zones are going to look great in stereoscopic 3D.
As for Dream Team, while I have been a fan of MarioRPG, since Legend of the 7 Stars and Paper Mario 64, Super Paper Mario and Sticker Star kind of gave me the impression that the series was going in a direction I didn't want to explore. When they first announced Dream Team I wasn't sold on it either. But watching the newest trailer in 3D on my 3DS, seeing with my own eyes that it's going to use 3D beautifully, AND go back to the traditional "team RPG" format that I love sold me on it.
I already knew I'd be getting a WiiU eventually and E3 hasn't really changed that. On the other hand, Sony used the conference to announce information I didn't have which convinced me to purchase a PlayStation 4 over an Xbox One (mostly pricing) as my primary console. Not an easy feat considering this generation I used a 360 as my primary console (superior controller, OS, and online experience) with probably 3x as many 360 games as PS3. Loved what Nintendo showed, but all had been officially announced for a long time.
If the price and fact that it doesn't have to be connected to the internet sold you on the PS4, that's your prerogative I guess. The Wii U already meets both of those criteria and released new information on far more games than the PS4, including many more exclusive titles, which makes me suspect it might have honestly had more to do with the whole (admittedly hilarious) "it's not the Xbone" hype.
Meeting the same criteria PLUS releasing more information on more new games seems like a winner to me, but to each his own, I guess? It's just a poll.