Here's what Gabe of Penny Arcade has to say about it:
I'm enjoying co-op and story mode, but that quote sums up why I'm reluctant to try SvM.
I feel like they forgot to mention the most important part- it is still incredibly fun and unique.
Ubi kept the essence of what made spies v mercs awesome. If it's not going to be any different, why make a new game?