As requested by Anon in another thread, I'm going to review Seraphim Call and Blue Drop. Note that I last re-watched these series already several years ago, and since my memory is shit I may not write all of the details, or some things may be wrong.
Seraphim Call
A single-cour original show by Sunrise, aired in 1999. It is episodic, showing stories featuring different girls each time who are apparently random, but surprisingly connected to each other.
How much yuri?
There is an explicitly yuri episode, some other episodes are pretty gay at plain sight, and there are a few where you need goggles. Be warned that there is a single het episode, and there are no relevant men outside of it.
Personal opinion
I consider it a hidden gem, most stories leave a message or make you think a bit, not exactly in a 2DEEP4U way either since it's pretty light; so regardless of its yuri content I recommend to watch it.
Blue Drop
The anime is a prequel to the manga, which was the original work from the author of the also popular "Two and Two" and "Sisterism" yuri manga. Aired in 2007, it gives an insight to the beginnings of the universe from the original work. It is a slice of life anime with cute and angsty moments alike. It depicts how an Earthling girl falls in love with an alien girl of the Arume race, a race made up of solely females.
How much yuri?
100% yuri. While it's not crude-sexual as the multiple Blue Drop manga or other works of Yoshitomi, there is explicit yuri by the end of the series. After all, it's a story of how these two females came to fall in love with each other.
Personal opinion
*read the spoiler under your own risk*
It is a pretty sad story, and throughout the anime there is always this weird melancholic aura, or at least that's how I perceived it, so it only made the end more depressing. The OST and OP/ED are GOAT, must listen. Some episodes are filler, and the pace is pretty slow, a lot of people might not like that. Despite its premise it is not an action anime, it's about 90% slice of life, so go read the multiple manga if you want action and smut. I warn you that the second manga spin-off has a genderbent MC (male to female). The manga are set when the Arume have already invaded Earth.