i bought hall of the mountain king recently.
In the end trans-siberian orchestra is pretty much savatage, olivia himself even says this and trans-siberian orchestra is qutie big.
I'm going to say that TSO isn't Savatage, it just shares the sound that Olivia brings to the projects he works on. TSO is too Classical/Holiday oriented to really be considered the follow up to Savatage. If anything, his 'solo' band, "Jon Olivia's Pain" is where Savatage went after Criss Olivia died and Savatage faded out.
Personally I like all the bands that Olivia has worked with, but early Savatage is my favorite for the raw metal sound. Music from that era was more raw, less synthy/overproduced (The Loudness war didn't exist yet!) and the progressive sound was still a minor influence yet. The late 70's through the 90's was an incredible era for rock/metal. (In all it's extremes, including things like punk.) Most things since then have been refinements/crossovers of those sounds and earlier. I doubt we will see any real major changes for a while now until the instruments that we use to make music change.
If anything we may see a bit of a breakdown in music (I think we are already seeing some of it.) where downloaded music has taken over but has been co-opted by old mainstream music industry interests. (DRM, RIAA, Clearchannel, etc.) That is to say, the potential new bands/underground music remains vibrant...but popular/mainstream stuff has tanked to the extreme.
Although speaking of bands resurfacing under a new name/sound due to members moving around. I wonder how many people know about the Demoniac-to-Dragonforce link? (Sam Totman/Herma Li)
From this:
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To this:
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You can hear the influences that carried over from the older band to the new if you listen for it.