The OVA has a much darker feel than the anime, which I prefer actually because I love the manga. Ever since I first read about this arc I've been hoping it'd be animated.
Episode 1 and 2 thoughts:
I wasn't really impressed with the first episode, but in the second when the real Syaoran showed up, I was bouncing off the walls with happy. XD I loved the contrast between him and clone Syaoran, and how rough he was in dialogue. The action sequence was amazing, and Kamui with his vampire twin... I know this arc isn't everyone's taste, but as a fan of this part of the manga I am extremely impressed with the OVA. I'll be chomping at the bit until episode 3 comes out.