I have actually wrote a few web components by hand in an environment where I didn't want any external dependencies and when that requirement was dropped I really liked how easy was to convert them to LitElement (and how much nicer it is to work with them).
I also have embraced the shadow DOM which is a default, but I think it's more trouble than it's worth. Now I use LitElement without shadow DOM and it works great as well.
Same about the shadowDOM. The only criticism I have about Lit is that the creators think shadowDOM is amazing and people not liking it are using it wrong. Lit lacks a good direction and someone with vision leading it but it became the technical pet project of a few.