When it comes to Septic Flesh, you should note that there is a gradual, but significant trend towards mainstream interest starting, if not on Esoptron, at least on Ophidian Wheel. By my standards, this only really became detrimental to the songwriting after the two aforementioned albums. Even on their lauded return to form (2003's "Sumerian Daemons") and recent works, structures and writing have become simpler, more rock-like. The band's main strength appears to be in the construction of simple, but powerful riffs and leads, which probably gives their pop music period an advantage over the CoF/DB school of symphonic metal.
Personally, I'd put post-1997 Septic Flesh on the level of later Therion - obviously diminished in comparison to their earlier works, but with good levels of musicality and some moments of transcendence. Definitely appealing to novices, and fans of symphonic metal, but rather predictable, and with limited shelf life. Then again, I have a very high tolerance for theater and cheese in my music.