The Nook HD is a 7 inch Android-based tablet with a high definition screen, just like the other two competing devices, and it starts at the same $199 price point. The Nook HD is expected to ship on November 1, which is about two weeks after this writing.
Should you go out and preorder one?
If you already own and like a Nook Color, this is a nice upgrade. You get a better screen, better battery life, and a lighter tablet. If you're not a Nook owner, or you're new to e-books, this may be a tougher choice. Let's look at the features.
Stuck With Barnes & Noble
Just like the Amazon Kindle Fire HD, the Nook HD is locked out of all things Google. You see, Google gives away the Android operating system for free and charges for the bits with Google, like Google Maps, the dedicated Gmail app, the Chrome browser, and Google Calendar. You can't download these items separately, because they're baked into the OS. So tablets like the Nook HD and Fire HD use a separate, proprietary app store. In the case of the Nook, it is the Nook store.
Part of locking down your tablet is intentional. You're forced to stay within Nook's app store, and that means your books and music come from Barnes & Noble, too. You're not totally out of Google. You can still use Google on your tablet's browser, and there are plenty of apps that sync with Google Calendar, check your email (even if it is Gmail), and do most of the other functional things you're used to doing on a tablet. The Nook comes with built-in Gmail and Microsoft Exchange calendar and email syncing. They just don't come from Google's proprietary code.
What if you already purchased books from a different e-book store? What if you want to buy a book from an independent seller that isn't tied to a book store? Barnes & Noble is also not as limiting in terms of e-book formats. Amazon uses the proprietary Kindle format, but just about every other e-reader out there, including the Nook, uses ePUB. That means you can sideload your books on the Nook by methods like loading them on the SD card, emailing them to yourself, or syncing them from your computer through the USB cable. The Nook has traditionally been pretty friendly to this. PDFs are also readable on the Nook (and on the Kindle Fire).
What you lose when you sideload is the ability to sync your reading progress across different devices. If your Nook is your primary reading device, this isn't much of a concern. Just remember where you've loaded your third-party books.
The new Nook HD isn't available as I'm writing this, but historically one of the big geek appeals of the Nook is that it was very hackable. It was pretty easy to root, and an entire user community evolved around the practice. Hacking your tablet is not for the timid. You risk ruining the device and voiding the warranty, but at $200, it's not total heartbreak if things don't work out.
The Nook HD starts out at 8 gigs of memory. This may sound like a disadvantage compared to the 16 gigs on the Kindle Fire HD, but the Nook has a microSD expansion slot. That makes the storage more flexible.
Family Profiles and Parental Controls
One of the interesting things the Nook has done better than the competition is make great parental controls. The Nexus 7 lacks them completely, and the Kindle Fire HD is making up for lackluster controls in the original Fire. The parental controls on the Nook Color are simple to use and cover things like purchases or Web browsing. The Fire promises to introduce things like time limits on certain activities that may give the Nook a run for its money - if they work as intended.
Another interesting feature for the Nook is multiple profiles. The Fire and Nexus 7 want to be dedicated devices with single users. The Nook HD is designed to be used by up to six different users with different bookshelves and media collections. This makes it very easy to let your child borrow the Nook without having said child rearrange all the books on the bookshelf.
One of the ways Amazon brought down the price on the Kindle Fire HD is by putting ads on it. You can pay extra to remove them, but the starting price assumes you want the "with special offers" version of the device. The Nook doesn't have ads on it.
No Strap, No Camera
The Nook Color had an odd little loop on the corner that you could attach a strap to. The Nook HD gives up this odd little feature in exchange for a sleeker look. Good choice. Most people probably would rather just buy a case than carry around a tablet on a strap.
Also missing: a camera. Unlike the Fire HD and Nexus 7, the Nook doesn't come with a front-facing camera for video chat. If your primary use for the device is reading books and watching movies, you won't miss it. However, if you ever video Skype, this could be a concern.
The Bottom Line
My recommendation is to still go with the Nexus 7, because it doesn't lock you into a proprietary bookstore, and you can get all the Google apps. However, if I were giving a device to a child, this would be a serious contender until the rumored 7 inch iPad mini is introduced, which may happen before the Nook HD even hits the market. Poor Barnes & Noble. They release an innovative tablet, and they're almost certain to be overshadowed by the bigger players in the market.