If you've played KOTOR, you'll love this one. Same combat style and interface, brand spankin new look.
Overall this game delivers on another solid example of what MGS can deliver internally. It has a great story with good twists and its nice to get away from the Star Wars universe, even if it is the same outter shell.
If you played KOTOR and loved it, this will keep you busy as well, and the differences will keep you occupied. It will last for about 10-20 hours, maybe more if you really press to do everything in the game. However you aren't really missing anything if you don't do side quests.