This is my biggest complaint as well, due to random migraines I wear sunglasses about 90% of the time when its sunny outside and I can hardly see the screen when wearing sunglasses, no issues with my n5, one max, m7 or evo lte. I wonder who manufactures these screens and I wonder if they have more than one supplier for their screens, I hope they do. Overall I do think the screen is more vibrant and better looking than the one on the m7 but this is a major issue for me as well.
Edit: Turned out to be a rogue screen protector, if you have a screen protector on try changing it out.