Yes, there is an unfortunate case of apparent insta-love. At least, it seems that way until you actually remember being fifteen, and getting those mad crushes for no reason other than the person is attractive and said hi to you as you walked past. The word "love" is never mentioned, only that Day has an inexplicable urge to kiss June (and vice versa) that certainly rings true in the context of their ages and respective loneliness. The blind faith June shows (at first) in the Republic feels equally authentic, as is her inevitable disillusionment.
The world feels well thought out, the characters well rounded. The pace is constant, high tension in nearly every page. I've heard the second is as good if not better - I can't wait (though I'll have to - there's a fairly long wait list for [b:Prodigy|13414446|Prodigy (Legend, #2)|Marie Lu|http://d202m5krfqbpi5.cloudfront.net/books/1336254717s/13414446.jpg|18712554] at the library).