After last penguin update, I see that on the 1st places for many keywords are youtube pages with poor irrelevant advertisement videos. I guess that is not very good for users who are searching for buying a product and at the top of SERP find only video advertisement. Or can it be only a temporary mistake?
If it is an advertisement then it is not necessarily the #1 result. Google has displayed ads before the 1st result on search pages for years.
The recent changes make many worthless websites went into the top ten. You can consider this as a problem accompanying the latest updates. Nevertheless, this can be seen in both the main and regional Google search results. When it comes to Youtube you can't forget that Google owned it and promotes their product.