Aria is beautiful, in both its character designs and its scenery. The music is relaxing and fits the relaxing mood. A pale yet colorful palette gives imparts a sense of fantasy to the series that really supports its more fantastical moments.
The characters are charming, if unbelievably naive and kind. Even the tsundere-type isn't abrasive, because if there's one thing this series isn't, its abrasive.The character interactions are interesting and cute, if sometimes one-dimensional; each character has a unique personality, but I couldn't help but notice that their personalities all seemed to revolve around one specific trait. Then again, that is how real people are, so I'm not going to say that their personalitites are unrealistic (except for the niceness part) in terms of their simplicity, I will only say that they are simple.
Aria: The Animation shows us the city of Neo-Venezia through the character's lens of wonder, and through their adventures and daily lives the audeince learns more and more about this idealistic, beautiful place. It is too perfect, and this fact sometimes distracted me, which is why this show can't really rank among my favorites. I will say, however, that for all the times I read that this show was really slow, I never found it boring. Except for one terrible, terrible episode. When you get to the cat episode, I recommend reading a book or something to distract you from how bad that episode is.
Anyways, in short, a charming and relaxing show, if not a truly outstanding one. Your opinion of it, however will differ from mine according to how stressed you are when you begin watching it.