To me, it's an OK song but didn't think it was all that; definitely not enough to become the official 2017 summer song (personally I think Stay by Alessia Cara was a lot catchier and more deserving of the title). But then again, it's got massive appeal internationally--especially all of Mexico, Central America, and South America. So even though it's not my cup of tea, I can see how the song got to where it is.
https://www.cnet.com/au/news/despacito-is-now-the-most-streamed-song-of-all-time/#
https://www.cnet.com/au/news/despacito-is-now-the-most-streamed-song-of-all-time/#