I think I can forge together some reviews again and I may even throw out a free request on Discord.

Wataru has failed to get into high school and while moping about trying to rediscover himself, he ends up in a place called Welcome House, home to 12 girls who all call him big brother and all shower him with unconditional love.
This is likely where the little sister fetish originated not helped by the origins of this franchise being routed in dating simulations. It's nothing like Happy Lesson where the lead can often draw from a well of mixed emotions, our lead instead is bland, boring and spineless.
But not all harem leads are interesting so what are our 12 girls like? After all it's the girls who are meant to attract the attention of the audience.
Well I can only really see two that stand out, Aria and Haruka, both of which stand out in a crowd of very cookie cutter female characters and even then they can barely hold my attention.
Half the reason harems are kept in single digit figures is to avoid personality overlap where the same traits appear in more than one character, in Sister Princess, the fact that they all display this diabetes inducing love for Wataru makes none of the characters standout, this not helped by the Anime lacking sexual tension which is what brings out the characters best traits in a harem; On their own, the sisters could pass for a side character in any other anime, here they are just the same character but playing a different person like a typecasted actress.
Speaking of which, despite a cast of good talent the dub is really bad.
The story isn't any better as the whole scenario feels convoluted.
Final Verdict: Sister Princess barely passes for fetish fuel, it doesn't excel in anything and fails to grab my attention.