To me, since I hate fillers, Dragon Ball Kai is essentially a new and improved Dragon Ball Z. The very title, the "kai", does mean "revision" or "remake", after all. I did notice a few scenes having been cut so far that were in the manga, but I don't mind those. Better to have a few cuts than entire arcs of filler episodes. It's only taken about 17 episodes to get through the Vejiita arc, which is half the time it took Dragon Ball Z to do so, and we're already halfway through the Freezer arc at just 26 episodes. Best of all, most of the old seiyuu came back to record the voices. New ones like Midorikawa Hikaru for Tenshinhan are pretty interesting. If nothing else, I had always wanted to see the Freezer arc in japanese, so I get that chance now. I get to see this series in the making, and just like for D.Gray-Man, there's a certain delight in that. Goku and Gohan's voice actress still sounds as good as ever, and I was surprised to find out that she is actually 72 years old.
So, what is there to say about Dragon Ball Kai. As a number of people will point out, it's harmless, silly fun, so you lose nothing in trying it out. But coming from a person like me who doesn't like series based mainly or solely on humor (ie, with basically no real plot), this is pretty high praise. The humor in Dragon Ball has always been just right for me, whether it's Piccolo's sarcasm or Goku's cluelessness. I've always had a fondness for Goku as a character from the moment I first saw the dub of the first episode of the first series. He's an all-around cute, determined, fearless, brave and often silly character. I don't see that he's changed much as an adult either, if at all. Goku has this sort of childish charm no matter what age he is. Despite Dragon Ball being a humorous series, it has achieved the perfect mix of action, lovable characters and humor. Generally speaking, this is just a fun series to watch. I can't wait to see the Cell arc, especially since I'm a big fan of Gohan. Hopefully they will use a song even half as worthy of "Unmei no Hi ~Tamashii VS Tamashii~" for the scene of Gohan's power-up against Cell in Dragon Ball Kai. To date, this remains to many the best song in all of Dragon Ball Z.