I have been quite surprised by how well this lens does for landscapes - comparing very favourably, when shot at F8, with the 35 and 55 EFs. Not quite as good but much closer than I would have thought.
I regard it as totally useable at all focal lengths in fact - something I was really not expecting to find.
Here is a gallery of mainly F8 shots, often of the same scene at different focal lengths, for those considering the lens for this use case to ponder. They are all LR developed with 60/0.7/70/20 and + 12 clarity, but with no lens corrections at all, either in camera or in post.
Crucially, I am starting to notice that the lens shoots a little wider in RAW than what you see in the finder, which seems equivalent to the corrected JPEG FOV. It also seems genuinely to shoot a little wider than its focal length settings. So, whilst I wouldn't go so far as to say yet (without testing to substantiate the claim) that the nominal focal lengths are 'after corrections', that's what I am tempted to believe. In any event, the weakest parts of the frames would be cropped off, had I applied corrections, but are generally pretty acceptable as-is.
Another reason I didn't correct any is to show that there is generally no point in correcting distortions in landscapes - so you can get the full bang of micro-contrast without worrying.
The files are all at 1/2 size, so equivalent to viewing at 50%. On my Retina screen at 100%, the originals all look good enough to make very nice large prints from. This is also a torture test in many ways: there is a lot of very fine detail in the shots and I think the lens handles them very well indeed.
Here's a link to the gallery - the 50% size files can all be downloaded.
And here are some samples so you can see where i was going with the 'one scene, many focal lengths' idea.