XBox - Ninja Gaiden Black
I finally picked up a console game and this was a good choice. If there is any question as to whether you should purchase this game since you own the original, then the answer is plainly "Yes".
Differences? For starters, anyone who was attached to having the Nintendo Ninja Gaidens available may want to keep their original. Black includes the arcade version of this Tecmo favorite, which I'm still trying to collect the rest of the Scarabs for. There are new items and a new weapon (Lunar), which make for some fresh action on this time around. The enemies are also noticeably more difficult. For example, remember those red dragon/dinosaur creatures? They now breath fire. There are also some added frames in the animation to add subtle spices to the new version.
For those who thought Ninja Gaiden was too difficult, there is the "Ninja Dog" mode. It isn't super easy, but it makes it more manageable to get through the boss fights. Ayane provides quite a bit of life powerups along the way as well. Dogs are also treated to a couple more FMVs, although I haven't seen any.
The mission modes are difficult, and will probably only be for Master Ninja Elitists.
This game is still insanely fun, especially when you hone in on your favorite fighting techniques. Give NGB a look.