I don't usually buy into the "L" hype or the "G" crave that Canon and Nikon has to offer, especially nowadays that third party manufacturers like Sigma and Tamron have lenses that are up to the premium-level glass of the first party. I've purchased two of the holy trinities from Canon before, finding them great, albeit very expensive (and justifiably so). I never really needed these zooms but I bought them anyway just for safety in unexpected scenarios.
The Canon EF 135mm F2L is a different story, though.
I have been lusting over this lens for a long time now, and I think this is the right time to finally have it in my kit. This almost-20-years-old piece of glass is nothing short of sublime IMHO. Although it's a bit long in the tooth, I find it to have the best resolution in comparison to other 135mm lenses I have used. It's built like a tank (very worthy of being an "L" lens), and the performance is excellent considering it's only costing me 70,000 or so Yen. Contrast isn't the best at wide-open like the modern Sigma lenses, but I can easily correct this in Lightroom.
It's all personal opinion here, but I sometimes find the 85mm FOV a bit awkward in that I find myself gravitating to my 50mm lens most of the time for portraiture (I don't shoot headshots, BTW). It's just how I shoot. The 85mm just does not get enough work in my kit to justify its value, so I decided to finally make the jump from 85mm to 135mm to make an obvious difference in focal lengths, hoping that I'll actually make use of this short-telephoto lens in the future.
Right now I find the 135mm to be a refreshing focal length to use. Other than portraits, I can use this lens to shoot some trains and some landscapes where I might need some compression.
I'm eager to see how this will change my approach to shooting different things :D