I am a sucker for a good 'second-chance' story, one where a circumstance--de-aging, reincarnation, time-travel, a wish, whatever--gives a character, especially a character like Severus who pretty much had a shit life in canon, the opportunity to try again, maybe with the deck slightly less stacked against him.
What I like especially about your story is that while the world Severus wishes himself into is, by almost any standard, a 'better' one than he left, it's still not easy for him to accept his place there, to fit in, to be happy. However miserable his old life was, it was still his life, and I'm glad you didn't gloss over that, or make it less than the *struggle* it logically would be to make a new one. I like that he doesn't just melt into a schmoopy caricature of himself, that he's still suspicious and insular, and snappish, and 'harsh'. He's not had much practice being happy, doesn't have much skill at it, and I like that he needs a lot of practice, despite having lots of help.
I also like your Lily very much; it's always nice to see her fleshed out, and she'd very appealing in her steadfast friendship for Severus and her obvious love for Harry, who seems just right--just what he'd've been like if he'd had that love, that security as he grew up.
And of course, yay for happy endings! And I'm glad that Severus remembered his wish at the end, mostly because I think that for such a very autonomous man, understanding he did, in a sense, create the life he is choosing, is probably necessary for him to be fully comfortable in the choice.