Based on first episode :]
Usagi drop is basically a drama/comedy. It starts with a "farewell party" for the main guy's Grandfather. There he learns that the grandfather recently had a child droopped off at his place. it was his illegitimate child. First ep is basically about the main character figuring for himself that the kid is really his grandfathers child and about who is going to take the kid home. No one had time nor cared about her so the main guy decided to take her home. I am guessing its going to be about him and his kid-aunt under one roof. it looks like it will be fun. Not hilarious but it will have a good serious story to it.
Edit:
I have watched 3 more episodes and I can honestly say I am loving where this is going. its calm, sweet and pretty funny. I love the way they ortrait the little girl. If you like a good story about a single dad and a lovely kid, this is a great story for you.