I actually really like most of Material Design. I often have to design HMI displays (user interfaces for industrial automation). There are good reasons for much of the design:
* colours should be limited and subdued for user interface elements so as to focus attention on content. Bright colours and animation are intended to call attention to important information.
* textures, gradients, transparency and drop shadow effects for the sake of visual flare cause visual confusion and eyestrain. Important elements get lost in the clutter otherwise
* ability to customize is often good but there can be too much of a good thing. If there are 100 "themes" or "skins" and all controls can be moved around by the user on a whim it severely detracts from usability. There is no consistency with the system and it makes it very difficult to train a group of operators when they all can mess with the UI. Also all the code that goes into extreme customzing is bloat.
* Skeuomorphic Design has no business in UI Design. If it was ever a good idea then MS Windows would have fully embraced Microsoft Bob to this day. Making controls look like photorealistic pictures of real life objects just causes frustration unless they behave exactly as the real object does, and are usually more cumbersome than what can be done on a computing device. Skeuomorphism is especially bad when it badly emulates something that is bad to begin with. Using a Blaupunkt stereo from the 1990s is a miserable experience in real life. Who was the idiot who thought we should have an audio player skin that imitates that crap?!
Good riddance to Bob, to Fisher Price gummi Windows XP and glassy Vista and 7. If you have to sit in front of that kind of garbage continuously for 12 hours a day as an operator in a power plant or refinery or whatever it is refreshing to see this "modern" trend. There are some teething pains as designers evolve, such as obscuring too many options or the wrong ones, lacking visual cues as to what is a control and font choices that are form over function as examples, but I for one am very glad designers are "growing up" and dropping the useless toys.