Welcome to the review. There are mild spoilers and a warning for the content. In western culture, a romance between an adult and minor or step siblings can be a bit controversial to say the least.
Plot: Natsuo is a high schooler experiencing the crushing despair of unrequited love towards his teacher, Hina. In an attempt to lift his spirits, he attends a mixer where he meets a girl named Rui. The two sleep together, expecting never to see one another again, but fate has other plans. His life suddenly becomes more complicated when his father comes home and announces he has remarried a woman with two daughters whom Natsuo has met before: Hina and Rui! Via Crunchyroll
Ecchi content wise - there are no nudity but I believe the Blu-ray versions will have some. This anime series has a lot of risque moments such as 2 sex scenes and masturbation on top of fan service. The art style feels josei or shoujo.
The anime's main focus are the three characters: Natsuo, Hina, and Rui. The anime adaptation cuts down on interactions and story arcs for supporting characters. Though, this might affect how you warm up to those characters as those story arcs have effect on how these three characters grow and advance their relationships between each other taking what they had learned. Examples of this would be Kiriya, Momo, Nac, Miu with Momo and Nac being love rivals to Natsuo and Rui's relationship dynamics. Miu and Kiriya (teacher and student) & Hina and her teacher portray relationships that contrast and foil Hina and Natsuo's. Though, as an anime only viewer, such changes are very unnoticeable. The manga is pretty similar in how it treated its minor characters, just supporting the trio, and to fade away except for the bar group. It helps that the anime keeps the focus on the trio while balancing the three. Natsuo isn't overshadowed by his two love interests.
Domestic Girlfriend is a soap drama that can be addicting if one grows attached to the characters. Your mileage will vary if you can immerse yourself with the characters and the taboos and challenges on their quest for romance.