Not horrible.
I like the fact that even though I hadn't seen the first episodes, I was still able to follow what was going on. The plot was extremely clear, and the characters seemed pretty in-character. The graphics were solid, although that sunlight-esque rotating piece when Sonic powered up was extremely distracting and seemed unneccesary.
In addition, the fighting sequence seemed extremely short, as did the entire "part" really. It felt like you could have had the fighting, either between tails and Sonic or Mecha (Why not Metal?) Sonic and Regular Sonic be longer. The fiht also made no sense, some of the attacks not seeming to inflict any harm on the combatants, and Sonic's blast of energy appeared to just disappear after hitting it's target for no adequately explained reason.
One plus point is that the music and sound-efferts is authentic and gave the whole video a sense of realism, which is always good.
However, I would prefer if you used dialogue instead of text. Since movies are a visual media, it's rather distracting to be watching a video while reading text, and you have to constantly shift from looking at the text and the video below. It ends up being extremely distracting.
Overall, the plot is good and the series has potential, if some flaws were resolved.