Except for the resolution of the plot, I hated it. Hated it.
For one thing, I hated the way the main character (and most of the other characters) talked. I have nothing against stylized dialogue -- two of my favorite movies are O Brother, Where Art Thou and Popeye (which I realize may be reason to discount my opinion), but the wa Juno talked didn't sound "clever" so much as "annoying". And the narration had an odd quirk in the deadpan-ness that had me longing for the naturalistic acting of Daria.
Also, a lot of scenes had extremely annoying music played over them, possibly to disguise the fact that nothing was happening. This was particularly vexing because the characters in the movie got to listen to cool music like Sonic Youth and Mott the Hoople. I mean, I love the Velvet Underground, but "I'm Sticking With You" is hardly the song I'd choose to underscore a scene.
I did like the resolution of everything. I thought people made good decisions. But up until then (and, indeed, after that) I did not care for it. I think it was mostly the script, because the performances all seemed fine.