You reaaaaally have to be open-minded when it comes to the OVA. For one, it's not a full-fledged anime, like Tales of the Abyss. Of course they have to switch some things around and cut things out. It's basically what Ryuryu said, especially when it comes to the animation. Compared to Abyss' animation, which I found to be a bit lacking, Symphonia's is just gorgeous because of the amount of time spent on it (or rather, because of how long it takes for each episode to come out, so yeah).
The animation has it's good points, but you won't find it if you're just close-minded about it, and fret that it's not like the game and it's 'too rushed'. It's hard to fit everything into ten episodes, after all, and back then they probably didn't even know that they were going to give it this many episodes.
Also, while it may not have been a full-fledged anime, it got more openings and endings than Abyss', and each of them are just as amazing as the nest. I can't wait to see the opening for this upcoming two episodes, and apparently there is going to be a different ending for each of the two next episodes (I think?) so if it is the case I can't wait to hear what the other ending it going to be.