Absolutely love this lens. I mainly use it for ceremony shots to get the grooms reaction when the bride is walking down the aisle.
Has a very distinct look to it, mainly because of the sharpness, good contrast, shallow DoF, and telephoto focal length.
I prefer primes to zoom lenses, so after owning the 70-200mm 2.8 II, I prefer the 135mm for my purposes. The larger aperture and sharpness of the 135mm are the main reasons for my preference.
The 200mm prime would be great, but so is its weight and price tag.
So, all in all, I prefer the 135mm at this time.