I think for me, V is the epitome of Symphony X. Possibly the newest album could upset that, if they can get the mixing and composition issues cleaned up, but until then, V it is. The Odyssey very nearly made me not become a fan of SymX at all. I'm NOT the only one this has happened to.
In fact, just yesterday, I met a person who was really turned off from Symphony X, by one song they heard recently. This person is normally OK with metal, but said that Symphony X, from that song, sounded "unoriginal", "the same four chords", "just guitars and drums". I can be pretty sure that was The Odyssey, because that's exactly what's wrong with certain songs on there--Pinnella's mixed so far down on some that you don't know there's a keyboard in there, and they just don't quite sound up to the level of their previous work at all. In fact, if I were a betting person, I'd bet the song they heard was "The Turning".
And BTW, what albums of Opeth have you heard? A lot depends on which albums you've gotten songs from.