What to say? What is a good speedgame? That is absolutely subjective. Personnaly I love it but others people don't.
What you need to know is that i is hard to learn. You need to consider that everything you know, or think you know, is bad. Your strats are bad. Speedrun strats are the absolute opposites of casual strats. It's long to run, which means it's EXTREMELY long to learn. But if you love this game, it will be alright.
That's only my opinion, other runners will probably give you theirs.
The biggest issue about Symphonia really is that there are a lot of cutscenes and not that much fighting for runs. However the fighting experiece (especially in NG) is thrilling. Really intense, technical and therefore requires to practice a lot. And I mean it. It takes forever to get good in this game, consiedring you both need technique and learning from boss patterns. And it gets even more intense considering most of the time if you die your run is completly dead, since you game over, no question.
So basically tht should guide your line whether you like it or not. Long because of CS, intense because of fighting, and also frustrating because if you die the run is straight up dead.
If you wanna get in Symphonia anyway, either in NG or NG+, it will require a really big dedication to the game, os get ready for it if you ever pick it up.
