My Summarit-M 90mm is a previous model, not the current. The largest aperture is f/2.5 while the the latest is f/2.4. That difference in aperture does not contribute a significance in image quality in theory. The launch of new version Leica M lenses means there are some improvements.
The latest of three popular M lenses: the Elmarit-M 28 f/2.8 ASAP, the Summicron-M 28 mm f/2.0 ASAH and the Summicron-M f/2.0 are examples of improvements. Apparently, metal lens hood has replaced the plastic clip-on. Of course the image quality has been optimised, such as the Summicron-M 35 mm f/2.0 features elven aperture blades instead of eight of the previous model, creating smoother bokeh, in addition to corner to corner detail rendition.
My Summarit-M is still sharp. if you use the digital finder EVF 2 to aid focusing when selecting the widest aperture. Summarit-M is the affordable range of the M lenses. It does not mean they are inferior. Thorsten Overgaard has tested several 90 mm M lenses and found the Summarit one performs well. You can also find very nice sample images on his post.
The Summarit-M does not look cheap, I mounted a metal hood on it to make it look more gigantic. It is not my daily lens. But it is a very good portrait companion.
The featured photo is a lizard I spotted on my front yard.