General Game Information
Controls
It's been confirmed that Punch-Out!! will be using motion controls - But it won't force you to punch your enemies for real. If you don't want motion controls on, you can just flip your wiimote on it's side and play as you would the NES classic. Balance Board support has also been confirmed, but with no further details.
Multiplayer
The first game in the series to feature multiplayer, Punch-Out!! for the Wii promises local splitscreen fights. Online has not been confirmed, and seems very unlikely at this point, but it should be noted that it has not been completely ruled out. Do not expect it to be in the game, however. As for the regular splitscreen boxing, the only character shown so far to be featured in multiplayer is Little Mac. Earlier on, it was hinted that the other characters would be featured in multiplayer as well, but it has yet to be officially confirmed. In a head-on fight between two Little Macs, one can transform into "Giga Mac" once they've gathered enough power, and the game then switches to single player view, where Little Mac tries to overcome the bigger Giga Mac. Giga Mac is featured in the Multiplayer trailer in the post above.
Features
The features have not been outright shown or stated, but it has been hinted that the game will have a lot of unlockables, such as new characters(presumably for multiplayer), new ring enviroments, challenges, victory animations and other things as well. It has also been mentioned that this is the first time that an internal Nintendo developer has run into space issues with the Wii's DVD, suggesting that they've smashed the game full with content. However, Super Smash Bros. Brawl was made on a dual-layer DVD while Punch-Out!! is made on a single-layer DVD, therefore it's assumed that this will be the most content-packed game for the Wii from Nintendo(spacewise, atleast) besides Super Smash Bros. Brawl.
Developers
The developers of Punch-Out!! for the Wii are Canadian development studio Next Level Games. They've previously worked on Super Mario Strikers and Mario Strikers Charged for Nintendo. Nintendo are publishing the game themselves, as they always do with their own intellectual properties, and Shigeru Miyamoto is serving as the game's producer.
Release
Punch-Out!! will release on the 18th of May, 2009 in the Americas and the 22nd of May in PAL regions. No specific release date has been confirmed for Japan, but it has been listed in several release schedules for 2009.
Rob Lowe, Nintendo's Senior Product Manager for Wii has said the following about the game's release:
"Punch-Out!! is our biggest Wii launch so far in 2009, and we see it as an important title that will appeal to gamers and families in a similar manner to Mario Kart Wii. It has a great pedigree with the previous titles on the NES and Super Nintendo, and this heritage is faithfully carried across to the new Wii version, along with a host of new functions and features. Punch-Out!! will be a full triple-A launch as you would expect from such a long-standing Nintendo franchise, and hopefully we will be looking at a number one position in the Wii charts around the launch of the game."
It has also been said that Nintendo of Europe have a massive marketing campaign planned, with the bulk of the spending being taken up by TV advertisements. Also, there is apparently a PR campaign that will take legendary real-life boxers and put them head-to-head in Punch-Out!! Wii's versus mode in the works. It was also stated that this is all part of a marketing tour that will be kicking off soon.
Reviews
The first review for the game was from Official Nintendo Magazine - 91%. A full transcript of said review can be found here: http://www.highdefgeek.com/viewtopic.php?f=16&t=8795 MANY thanks to VGChartz user digitaledge81 for said transcript.