Oniichan no Koto nanka Zenzen Suki ja Nai n da kara ne!!

Well Lets see.. They both have that "incest" Vibe to it. Although, I do think that OreImo Has a more sensible relationship between the siblings and actually has some sort of story. Onii-Chan no Koto goes abit overboard with the whole Incest thing. Also, it's animation is abit... Strange? OreImo Revolves around the relationship of the brother and sister and the whole otaku culture. Where as Onii-Chan no Koto revolves around more sexual jokes, stronger incest content and this strange harem. Personally, I enjoyed OreImo more than Onii-Chan no Koto, But im sure if you liked one, you may enjoy the other.  

Both have REALLY long titles Both have potential incestuous relationship between brother and sister 

Both deal with "sibiling" relationships, and trust me both are really good!! 

Both are anime about a little girl who wants to have sex with her older brother. 

About younger sisters for a start... Harem, brothers who have a friend that are fujoshi, not dubbed yet, and hilarious. 

Step-siblings, the girls' feeling are some toward to their brother. 

Fan-service, ecchi, and "siblings relationship". Yup, both of these series has all that. The girls in both anime goes after the main protagonist in ways that are embarrassing. Although not technically blood related, these series has the girls going after the guy many times. If you're looking for a real storyline development, then don't just toss this out trash but if you're looking for some fun entertainment and guilty pleasure, then keep these two series in your watch list.  

Both are incest anime about a boy and his harem of women to include his sister(s). 

Both series seem to follow a Brother-Sister and Sister-Brother complex that drifts a far. Incest theme. Forbidden love. 

Both are about a little boy main character and his harem of women to include his sister. 

Both are ecchi harem series that have a perverted sister who's trying to get with her brother. Although, Onii-chan Dakedo Ai Sae Areba Kankeinai yo ne has better art style. 

Both are about a perverted sister trying to get their brother to fall in love with them, with a harem sub plot.  

The animes are very alike involving step sisters trying to get with their step brothers. While encountering rivals for their brothers love along the way. 

very similar in incest and story but onii-chan is more on the comedy and the animation is not a good 

Perverted girls, wanting to get laid with the main male lead.  

Very energetic main characters who's main goal is to be perverse with guys of there liking. Dimwitted but well meaning male leads and some interesting secondary girls to keep the shows fresh and entertaining. Lots of classic styled harem scenarios with one or two new twists on a very used genre. The shows are full of perverted humor and strange things happening all the time. The main difference is B Gata is a much more well developed show when it comes to characters not just in one aspect either. The Art,Back Story and originality is much higher quality.