Although RTW was great progress in some aspects, I never liked it so much because of the small tech tree and the boring restrictions to unit diversity. Ok, that was not a fault of CA as there was no similar development of military technology in the antique times compared to the medieval ages.

Apart from that what econ21 rightly said M2TW is RTW with better technical development, more different troops (although not enough) and a special goal at the end (new world).