I find Severus as Harry's father stories so, so interesting, because the mere thought of how differently everything could have gone had Harry a strong, determined role-model, just breaks me. And your story just had so many *moments* that delighted me.
I loved the mention of Minerva checking up on Harry, loved how Severus played on Petunia's maternal instincts to gain admission to Privet Drive, and loved the bleeding hearts pinned to the door. Slytherin valentine's, indeed! Hehe.