For starters there done by the same writer, but also they have practically the same vibe to them. Both feature
A tsundere sister who is in love with her brother (Happens later in ore no imouto, sooner in Eromanga)
A surprisingly patient main character who takes alot of crap
Both are also have a harem vibe to them without executing it properly
In a whole i would say Eromanga is better since i dropped ore no imouto because it bored me.
Either way if you came for the incest kinda vibe you will like both
-Both Protagonists have sisters with weird hobbys.
-Both Protagonists, in a way or another, discover this and had to keep it as a secret.
-Both Sagiri and Kirino have the same plushies in her beds. (Not relevant but interesting)
Eromanga sensei is the living reincarnation of Oreimo. Both MC's in the show are very caring towards their younger siblings or let's just say they very much love their cute and loving little sisters. Both the shows involve an incest relationship although in Eromanga-sensei, they are step-siblings and they're the only ones in their house because their parents was involved in a tragic incident. Both shows are great but if you want a deeper and a better plot, I'd recommend to watch Eromangaa Sensei.
There is a strong emphasis on the creative process -- how manga/light-novels are inspired by the people around the author, and whether the authors actually understand the nature of the relationships they write about.
Of course, there's also romance, confusion, strange people doing strange things, etc. In these areas the anime go in very different directions, but that's fine.