STORY: A pretty original story, if I say so myself. Most sports anime that I've seen focus on a newbie that ends up being great at the sport they play - with little to no training beforehand, or at least no real training. This was a bit different in that the main character started training to play the game when he was a toddler. I can't say much more about the main guy's background without spoiling things. In short, Prince of Tennis about a kid named Echizen Ryoma who enrolls in Seishun Gakuen and joins the tennis club regulars to improve his tennis skills - and become more than just a carbon copy of his father. Seems simple, right? Wrong - if it were that simple, there'd be no need for almost 200 episodes. Prince of Tennis is about more than Echizen Ryoma working to become #1 - but I can't get into that without spoiling it.
ART: Pretty amazing, to be honest. I remember other anime from this time period, and their artwork wasn't nearly as good. Sure, there are some repeated frames - but that's almost impossible to avoid in lengthy anime. The character design was done especially well - and with such a large cast, good character design is a must. It's no good to have a large cast if you can't even tell the characters apart, so kudos to them for actually making them distinguishable.
SOUND: Some of the themes seemed like badly done karaoke songs, but some of them were actually pretty damn good. Out of the ones performed by actual artists, I'll be honest and say I only liked the ones by Kimeru and the final OP "Dream Believer" - but I liked the few songs that were supposedly performed by the characters. However, that's the best thing I can say about the music. The sound effects throughout the anime were pretty good as well.
CHARACTER: With such a large cast of characters, it's hard not to find one that you like. It'll also be hard to find one you can't connect to (I personally can relate to Fuji Shuusuke pretty well). They are extremely well-developed, but unless you stick with the show for the long haul - you might not be able to see it. The creators give each character their own was of playing tennis - including the people that mainly copy other players (and that's saying something). It's difficult to give each character their own personality if you have too many, but somehow the creators of this anime managed to do it. Yes, there are some characters that are similar to each other - but that's unavoidable; however, even those similar characters have subtle differences in their personalities that make them easier to tell apart.
ENJOYMENT: The anime is very enjoyable, provided that you can actually sit through 178 episodes. If you don't have the patience for it, then it's not as fun to watch. And when I say patience, I mean sit through the first 10-15 episodes before deciding whether or not you want to watch it. Believe me, when I got to about episode 11 - I wanted to quit watching, but I eventually got through it and once I reached episode 15, or something like that, I couldn't stop watching. Even the filler episodes are enjoyable to watch - and for most anime, you can't say that.
OVERALL: A very good anime overall. It starts off a bit slow, but stick through it - and you'll enjoy it quite a lot in the end. I know I did - working on the OVAs right now, actually.