I remember first seeing this at my first anime con back in 2003, and after watching it, I immediately went out and bought it. I absolutely adore this OVA and have watched it so many times I basically have it memorized.
But what makes it so good? That's kind of hard to explain.
First off, it only has about a 40 minute runtime so it doesn't overstay its welcome. It has a very wacky, comedic pace, but also has some tender moments in it. The story it is telling lends just enough for 40 minutes to be perfect. Another series Shirobako tried to do the same thing, but it was 20 plus episodes and couldn't capture the magic that this OVA did.
There are just enough characters to be likable and memorable, but it doesn't overwhelm you with 30 plus characters (coughshirobakocough)
Next, the zany humor works perfectly with the plot of the story. They never go too overboard and know when to real it in. I have heard both the Japanese and the English dub, and while I can say I prefer the English dub more (Lisa Ortiz ftw) the Japanese isn't bad either. Both bring different performances and both work.
One of the reasons this is such an underrated OVA is because it was released by Central Park Media which, unfortunately is no longer in business, but even when they were, only a handful of their shows ever became popular (example, Slayers, Utena)
But this really deserves more love than it gets. I hardly ever give animes straight 10 out of 10s, but I still love this to this day and watch it whenever I am feeling down. This was a spoiler free review because I am telling you to GO WATCH IT!