I really like the 40-43mm focal length for a fixed lens body - much more versatile than 28mm which pushes you to the wide end for all shots. In this regard I like the Q3 43 much more than the 28mm version.
I do think that Leica has missed an opportunity here though and agree with Ko.Fe that the lens is just too big and unbalanced. When I think fixed-lens; I think of an EDC (Every Day Carry/Camera), a travel camera for somebody who doesn't want to carry much gear, or a camera for people who want only one camera they can pick up at a moments notice. In all these scenarios compactness is a desirable feature. The 40mm focal length seems to have the greatest ability of being shrunk to pancake size, yet here it's huge. Leica can make great, sharp, tiny non-apo lenses (40mm Summarit f2.4 on the Minilux for example or the 40mm Summicron M lens). I don't think making the lens APO or 1.5x Macro justifies the large size in this context.
Perhaps it's as Ko.Fe says; it's the AF machinery that makes the lens so large?