It is unlike haruhi, which is a good thing. It simply means that she has changed (and she should, because people do), and it just so happened that this change is her liking Tamaki. I honestly think this has happened too late. If they showed a bit of development between the two a few episodes ago it wouldnt have been this abrupt. But I still think its one of the best developments in the series.

Oh and by the way, the other girls are also different from eclair (who is a demon bitch) because of the fact that she seems to exert control over Tamaki, which no other girl (except Haruhi herself) has been able to do in the series. It would make sense that she got jealous because of that.