Lusted, I played about 100 turns of a Parthian campaign and noted a couple of things you might want to look into if you're planning another release:
-- The new eastern forts (the stone ones with big walls) are buggy -- the walls can't be battered down with rams, but the AI thinks they can, so they sit there battering with their rams (which are half inside the wall, since the wall is so much thicker than the old wooden ones). These should be replaced with the original forts -- they look great but play horribly.
-- Something is odd about the region on the south-easternmost edge of the map, it kept rebelling from the Seleucids and becoming Parthian, and giving me high-level units every time it switched (at one point four or five 'General's Bodyguard' units appeared after it had rebelled!) -- I had to ignore it and pretend it didn't exist for reasons of gameplay, didn't want any advantages vs. the Seleucids.
This was on a H/H campaign using the RTW .exe (not BI).
Oh, and I've said it before, but I'll say it again: TE is one really amazing piece of work!