The Good: Clean shifts, reduced chain slap, different cage lengths
The Bad: No clutch, no barrel adjuster
This derailleur showed up as an OE part, but the XT name is always appreciated when looking into Shimano parts. This derailleur is a good mid to mid-high level 9-speed derailleur option. On the trail the derailleur is very quiet and smooth. The Shadow Tech does a really good job of limiting chain slap, I only really hear noise over the really rough stuff. This shifter also moves very well. If you have it set up properly you won't find this derailleur under shifting or over shifting.
One complaint would be the lack of a clutch, found on the Shadow+ derailleurs. I know you can get the clutch with an upgrade, but it would be nice if Shimano had one derailleur with all the tech in one line instead of 2 or 3 different derailleurs under the XT name. My other little gripe is no barrel adjuster on the derailleur. I know this is kind of an old school thing, but I always liked having the little extra bit of adjustability if the barrel adjuster at the shifter wasn't enough.
Overall another awesome derailleur from Shimano that would be comfortable on anything from am XC to a DH bike.