The series description made me think that Yuzuya's presence would be a plot device which influenced the major plot line of the series, Kippei's love life--but in fact, Yuzuya and Kippei's love life are both major plot lines. Yuzuya's more so.
The series has many similarities to Kare Kano. (It's not a masterpiece like Kare Kano, of course.) It's about people who discover or explore what it means to have love, romance, and family. The way the "love" theme was handled also reminded me a bit of Eternal Sabbath (not the main themes of ES, but the lesser ones). The friends and siblings of the major characters also have their stories (relationship drama), which are usually light and brief. Most plots developments in Aishiteruze Baby just concerned the main 2 plot lines (Kippei's love and Yuzuya).
At the start of the series, Kippei is just a "player", but caring for Yuzuya brings out his mature side. Because the form of Kippei's romantic drama is ambiguous until one or two volumes into the story, I can't speak about it at all and thus will have to skip past many of the positive points and onto the other main plot line, Yuzuya. Therein lies my one major complaint about the series: Yuzuya is clearly is her own unique person capable of emotional problems, but many times her behavior and reasoning felt caricatured into order to act as a plot device. In other words, I wasn't too into Yuzuya, although the relationship between her and Kippei was really cute. Also, the rhetoric of this manga didn't impress me, though it wasn't bad.
Well, I didn't read it for that: I kept on reading because I really needed to know how the romance turned out. In any case, I hope what I've said doesn't come out negative because it would spoil the first two volumes for me to counterbalance my criticisms by talking about the romance in enough detail to praise it. And just because I've criticized an aspect of part of the plot doesn't mean I didn't value or enjoy that part of the plot as I experienced it. All in all, Aishiteruze Baby was a very enjoyable read for me.