Overall I thought this was OK, mainly because being an adult I didn't take it seriously. The acting was alright and I thought Juno was sweet.
I am surprised Kim Hye-sung has not gone on to do a lot more.
As for the issue of teenage pregnancy, it could not be made fluffier if they tried.
The idea of a 15-year old, handling such a big secret in this way, is ridiculous.
It was all just too fantastical for me and lacked substance.
The film was a mess really, not funny enough to be classed a comedy, not tense or emotional enough to be a melodrama and not deep enough to be a decent drama either. That was a main problem.
Either write it as a comedy, in which case keep it light, avoid the issue of abortion and make the main characters older by a couple of years.
Or, make it a serious piece of work on a difficult topic and have the characters go through what would be an incredibly traumatic experience for all concerned, in a realistic way. That would need more focus on the families and less on their peers doing strange musical type turns and behaving like their friends had just won a teen idol competition!