Knights of the Nine had everything that you could want. Possibly been the most fun I had with Oblivion.
This add on had a bit of everything. You get a really cool set of armor, some new weapons, some amazing locations and a really nice storyline to go with it. You will definitely get your moneys worth for this add on.
One of the best things about this package is the downloadable content. It doesn't matter if you are a wizard, a thieve, an evil vampire or just some dude who owns a horse. No matter who you are, you will absolutely like what the downloadable content has to offer.
No matter how you play Oblivion, you will like Knights of the Nine. It may or may not be a short experience for you but when I look back from playing it, I reckon it was pretty good while it lasted.