The EF 135mm f/2 L is probably tied for first place in being my favorite lens (alongside the EF 50mm f/1.2 L). So before I make to move to mirrorless, I was waiting for both these focal lengths to have an RF version.
Love that it now has IS and that it's weather sealed.
The minimum focusing distance of 70 cm (vs the EF's 90 cm) along with the slightly brighter aperture of f/1.8 means minimum DOF is down to a mere 2.3 mm from the EF's 4.5 mm. Awesome!