This site gets the details right. Every book also has a beautiful cover made using public domain artwork. Books are proofread by an actual human, meaning there aren’t weird typos caused by the scanning process. Everything has complete metadata. And there are platform-specific downloads for Kindle and Kobo, meaning all features of those platforms are properly supported.
Not every public domain book you could imagine is offered, but a surprising number are, and it’s growing thanks to a team of volunteers. My suggestion: if you want to read a classic book check Standard Ebooks first, then head to Project Gutenburg if you can’t find a Standard version.