Lots of different artstyles can be beautiful and serve different purposes.
One of the most beautiful series I've read on here would be WataTabe by Naekawa Sai. It's not exactly unique in its approach (unlike BlueDsc's recommendation), but it's got some fantastic designs and detailing and meshes well with its rather creepy and unsettling undertones.
For something completely different, yet visually super appealing to me, I'd point you to Blue Skin, Big Tits or any other works by Zyugoya
The next one isn't yuri and once again quite different, yet also one of my favs in terms of art: Torako! Don't Break Everything!, a rather zaney slapstick comedy.
I also can't help recommending a look at Itou Hachi's work (here's a harmless, wholesome example) because I really do find her art extraordinary.
More typical again, yet also kinda striking, is IMO Yoshitomi Akihito's work which looks cleaner than the previous two, but is also quite opulent at times and decently recognizable.
Also, if you want to see how downright beautiful hentai can be, I'd recommend looking up Jorori's works.