Story: The story is a little confusing to me and doesn't quite get as explained as I would like. I don't think they should just leave the manga to do all the explaining. That being said, the plot was deeply engaging. I wanted to keep finding out the gang's adventures. I'm not usually a fan of fantasy and was actually not going to watch Tsubasa. However, I heard that it fits well with xxxHolic (which I love) so I gave this a chance. It truly impressed me and I love the plot. The tragedy that is the relationship between Sakura and Syaoran is heart wrenching but engaging. I really felt for what was happening even if I didn't completely understand everything. Fillers were fun but still felt like fillers. Furthermore, the story had humor, drama, romance, action and fantasy and good quantities and qualities of all of those elements.
Animation: Beautiful animation. The character designs fit to a tee and are just amazing, as what you would expect from Clamp. All of the character's are colorful and memorable. Some of the eyes feel like they're reused though. Male and females are equal in quality. The action scenes are fluid and engaging. Colors are bold and bright and the scenery for all the worlds are unique and remarkable. I have little bad to say about this animation.
Sound: AMAZING. PERFECT. LOVE. Hands down, the best music I have heard in an anime. Yuki Kajiura does magic. The opening and ending are great but pale in comparison to the instrumental. I have little anything to say but amazing things for this music (hence the 10). However, I was not in love with some of the music from Oto country which as essentially the same but with jazz twist (it wasn't my personal preference but it wasn't bad). I would recommend watching this series for the audio alone and I plan on buying the soundtrack. In addition, the seiyuus fit their roles in both the original and the English.
Characters: The characters's quality is in between that of the animation and that of the sound. In other words, you've got some stellar characters. All of the main gang is developed quite nicely throughout the series. No 2-D characters here. They all have such depth and are endearing. I fell in love with them, their stories, and their works. They all play great roles and are not overshadowed.
Overall: Amazing audio, characters, animation and story. I would recommend this to about anybody because it really does encompass such a broad scope of things. Definitely a favorite and I would watch this over again.