Just yesterday i fought a chap (whos first game i assume it was) who took 10cilibans (very heavy cav) put them all in one big wedge and rolled over my entire army.
Maybe is just me, but I assume that in BI you are able to win this with nice balanced army (you just move units a bit differently then in mtw/vi) which was not possible in RTW. Imho.

Maybe we will see players coming back to VI, but I still belive that BI is a step in right direction. For me problematic issue is lag and replay desync.