I watched all Da capo series (up to DC III minus DC If) in one run, so this will cover a bit DC II as the prequel and some of its parent stories.
This is the only aspect why I follow through all DC series. The story from DC I captivated me a bit and it's even better in D.C II (especially SS). The mystery behind the never-withered Sakura tree is handled fresh in each series, a bit connection from previous story but still original. This is pretty good considering how many stories have been produced for this sakura tree.
In short, It's better than DC I with more vibrant colors imo.
Opening is good (DC II SS), but others are really weak to leave impression on me.
This is the worst problem with DC series. Almost all characters are mediocre at best. I have never seen any other MC in other series as boring as Yoshiyuki. Frankly speaking, I'm sick of this "A popular guy who is kind to everyone but dumb enough to realize other's affection". Any cliche situations can be found here and the most annoying thing is when that MC being dragged around by his friends without being able to decline. Oh, man.
Junichi from DC I is a tiny bit better for me considering his sense of humor, but Yoshiyuki is REALLY boring, except when the series reaches its end where the sadness built up.
The only interesting characters for me are Minatsu which is handled much better than its counterpart, Miharu from DC I and the Asakura sisters (but only near the end). Beside that, mediocre to the letter.
I really don't understand why this is called D.C II SS. Except the same characters, everything from DC II seems dissapear without explanation. The most obvious one is Yoshiyuki's relation with Koko. Well, they mention it a bit in ep 2 (CMIIW) but after that, she was thrown away from the story. I really hope that the relationship and the problems could contribute in either adding more flames in the conflict in SS or solving it.
Shortly speaking, I think I will feel better if I watched DC II SS without watching DC II.
This score is for DC II SS WITHOUT DC II because as I say, there is no important continuation whatsoever, including the plot. I really love how they built up the tension towards the end of the series. The road to climax is really good and tear-jerking. I would be glad to give this 8 or 9 if the ending is not as cliched as it is. Sola's ending is waaaay much better than this.
Good story, nice plot, boring characters, and horrible continuation. Well, at least I enjoy the story.
Shortly speaking, it will be good series if there is no DC II and they handle the characters and the ending better.