I finally broke down and bought BI.
I'm so far impressed with what I see.

In one game with the Huns, my Hordes just completely overran Constantinople. However, I do see the problem of Hordes being way too powerful. If you take Britain from the WRE, that will trigger the spawning of the Romano British faction Horde, which will march on London. Unless you are prepared with a huge army, you will be quickly overrun.

Night battles are cute, but I have yet to see one where it's useful.

OMG! Shadows! No longer does marching through a forest look like you are marching through a bunch of 2D sticks in the ground. The shadows of the units and the forests REALLY make it a visual enjoyment.

The difficulty of playing the WRE can only be summed up in one quote:
Quote Originally Posted by Garvanko
I almost cried after turn 1.

If you are looking for a good challenge, or at least something refreshing, I suggest picking up BI.