I'm a Sonic fan, and I have been for a long time, but to be honest, I didn't really like this, and here's why-
Story: The story for the Sonic OVA/Movie is just like any other Sonic franchise, Sonic has to stop the villains no matter what cost. The story was very strong. You have Sonic and Tails at the beginning looking out for villains when they stop into Robotnik. Apparently Robotnik has "captured" the Mayor and his daughter. Suddenly, a robot named Black Eggman (or Metal Robotnik in the dub) appears in Eggmanland (or Robotropolis in the dub), and Sonic then goes to defeat the robot. Little does Sonic know that this is all part of Robotnik's plan to be able to collect Sonic's mind and thoughts in order to make a replicant of Sonic, called Metal Sonic. So now Sonic has to save the mayor, defeat Black Eggman, and defeat Metal Sonic. The story's as any other Sonic game. A strong one I must say.
Art: The art for the Sonic OVA was bland, and not colorful. This is probably because the show was produced in 1996, but Serial Experiments Lain also came out at that time, and that had amazing art. Anyway, the characters themselves do look like they were intended to. I wish they took more time on Knuckles and Robotnik, because they didn't look that great. The background design also needed improvement. There was a part where apparently Sonic and the gang were near a volcano, and lava started to pour out. All you get instead of good background details, it looks more like water with bad photoshopping. Anyway, the art was good, but there needed to be improvements.
Sound: The sound for the OVA wasn't that good either. I do think you could hear them, but not always. The voice acting for the characters were good. The Japanese voice actors were good, but the dub actors needed improvement. Dub Sonic sounded whiny, dub Tails sounded like a 4 year-old with a cold, dub Knuckles sounded too calm and needed some anger management, and the only voice actor that was good in the dub was Robotnik's.
Characters: What can I say that hasn't been said about the characters? Sonic's cool as always, Tails is a great supporter, Knuckles was a good character, and Robotnik and Metal Sonic were great villains.
Even though there was a great plot and characters, I didn't really enjoy it. Honestly, I was bored and was anxiously waiting for it to end. They took too long on how Robotnik was able to make Metal Sonic, and the parts with Robotnik and the Maoyr's daughter that was intended to be funny, just bored me and made me want to take a nap.
Overall the Sonic OVA was just average to me. They could have done better jobs with this. Die-hard Sonic fans will love it. If you're not a fan of Sonic or you don't know much about Sonic, I wouldn't recommend it.