I rented this simply because the box looked nice. I wasn't expecting it too be all that good. Boy was I wrong! I watched it four times, and then came to Amazon.com to buy both tapes.
The animation is excellent. It's easily on par with that of "Ah! My Goddess!" The amount of action is incredibly too, including several superb fight scenes. Most anime will show the same punch from 3 different camera angles or show a still-frame of the character on a moving background, but not Birdy. All the action is wonderfully drawn and acted out.
While the plot is only fair, the concept behind the plot is very cool. There are a few instances of jokes or lines that don't translate well, but even they aren't too bad.
The character Tsutomi was a bit too whinny at times. However, all the other characters, even the extras, were very good. The best character of all was Birdy. Her voice actor was simply amazing. You can feel the frustration, relief, etc. in her voice. The artwork for her was very, very good. I would love to see more characters with two-tone hair.
One last thing I should mention. Birdy has several rear nudity scenes, but no hint of sex. It's not that bad, and would only upset a very puritanical person. (Actually, old Loony Tunes episodes had rear nudity at times, and they've been shown on network TV for decades).
In almost every department, Birdy the Mighty is superb. I haven't seen anything I like better. My only wish is that the series was longer.