Angry Birds HD ($4.99) by Chillingo Ltd is a physics based puzzle game where you launch birds at structures trying to knock them down. In the structures are pigs who ate the birds' eggs, and that's why the birds are angry.
The game itself: Angry Birds HD is the same exact iPhone game, just with iPad native resolution. All of the over 100 levels are exactly the same with nothing new for the iPad version. It's an amazing puzzle game on the idevice as you launch birds at all kinds of structures to knock them down and get revenge on the pigs who ate the birds' eggs.
One major disappointment with the iPad version is that the interface didn't even change so you still can't see the structure you're firing at without pinching to zoom out. You would think with the extra room they could have redesigned the game to see everything at once, and not just enhance the graphics.
The game has the same limits of the iPhone version despite working on the iPad which gets rid of those limits. The problem with the iPhone version is still in the iPad version, and the lack of innovation is severely disappointing.
If you own the iPhone version: If you already own the iPhone version there is no reason to buy Angry Birds HD for $5. You can play and should play the $1 iPhone game in double pixel on your iPad as it looks about the same since you'll need to zoom out on the iPad or iPhone version.
The levels are exactly the same as the ones you've already played, and the interface of not seeing the structure you're firing at is sadly maintained. This is one HD app that isn't worth the price of the upgrade.
If you only own an iPad: If you only own an iPad Angry Birds HD is one of the better puzzle games available though there is the frustrating aspect of always pinching and panning the screen to see what you're firing at. You could even buy the $1 iPhone version, and play it at 2x to get practically the same experience, and save yourself $4 in the process.
If you never bought the iPhone version: If you never bought the iPhone version it's a great time to do so. It's a great physics based puzzle game with over 100 levels. See our review of the iPhone version to help you make the decision to spend the $1.
Words With Friends HD ($1.99) by Newtoy Inc. is a Scrabble like game where you spell out words crossword style. The game is distinct by letting you play up to 20 games at once at your own pace.
The game itself: Words with Friends HD is the exact same game as Words with Friends, but the board fits the iPad screen natively. The game is exactly the same allowing you to play up to 20 different games at once at your own pace, and you can chat with any of your game mates. The iPad version puts your other games, and the chat screens over the main interface, and you never have to zoom to add tiles in precisely.
With that said it doesn't change much at all for the iPad. There is no functionality to let you play with people right next to you on the same iPad. On top of that the iPhone version at 2x provides the same advantages of not having to zoom in. This is one game that doesn't look really different with the "HD" moniker.
Also currently the game is experiencing major slow downs in connectivity so it takes awhile for the game to load all of your current matches. On the iPad version the push notifications are malfunctioning so you never get any pushes from words with friends, though you get them from all your other games.
If you own the iPhone version: If you own the iPhone version of Words with Friends just install it on your iPad, and you're good to go. You have the full interface so you don't need to zoom in, and it looks practically the same running at 2x. The iPad version is the same price, but there's no reason to buy it again, as the iPad version's pushes don't work.
If you only own an iPad: If you only own the iPad you might want to wait to buy Words with Friends until the push notifications are fixed. NewToy has already released an update that alleges they're fixed, but still not one push from the game even with it turned on in the settings. Also the load times are a pain, so this game isn't ready for prime time, and your money.
If you never bought the iPhone version: If you never bough the iPhone version you should definitely look into it as it's a wonderful take on Scrabble. It lets you play multiple games at your own pace with push notifications letting you know when it's your turn, which are vital. Check our review of the iPhone version to help you decide.