This drama is very good and in some ways reminds me of Otousan, such as Natsuo having to deal with his younger sibling's issues and being helped along the way by Yuki. Also like Otousan, this drama is both very funny and very heartwarming, though it's also bittersweet. What I really like about this drama is that none of the subplots drag on for any longer than they need to, like Jun wanting to become a teacher and the fight for Chika to keep her baby. The romance between Natsuo and Yuki was sweet, charming, and heartbreaking.
I like all the characters. Natsuo is a solid character, very mature and learns how to be a father to his younger siblings even though he was really a bit too young to really be a father. However, I will say that Natsuo was at times annoying when he acted like a loud chatter box. For Tsuyoshi, this is a better role than he got in Moto Kare but I still like his character better in To Heart. Ryoko's character was cute, sweet, and really unselfish. I'm really starting to like Ryoko more and more after watching her in this drama and in the French movie, Wasabi. I was really impressed with Oguri Shun's acting in this drama as Natsuo's hearing-impaired younger brother, especially after watching him play a much different roll as a ruthless gangster in Smile. He really pulled off two rolls that couldn't be anymore different.
On the downside, I found a couple of the characters to be annoying, especially Chika and Seiji in episode 9. The ending was also a little bit too bittersweet, and I felt that this drama deserved a much better soundtrack. Moto Kare, another drama with Domoto Tsuyoshi and Hirosue Ryoko, had a much better soundtrack despite its bland story. If only Summer Snow had Moto Kare's soundtrack I would have liked this drama much more.
Still, despite some of the flaws I really liked this drama. I give it a solid 8.5/10 and recommend it to any jdrama fan.