After about 10 years I'm finally giving the main quest a dedicated crack and I'm at the point I've just been told to go to Kogoruhn, how much longer is left?

You've still got quite a bit until the grand finale. Without spoiling too much, right now you're proving yourself as the Nerevarine to one Ashlander Camp. You'll still need to do the same for the remaining 3 as well as the 3 great houses (which requires a lot of running around.) Once you do that, theres still a few more fetch quests before you can make your way to final boss!

Quite a bit left. You're at the "Third Trial." You must still do the Fourth and Fifth (getting the support of the ashlander clans and becoming Hortators of all three houses) before you "qualify" to be the Nerevarine, and take on Dagoth Ur.

wow awesome!