Our artists did an amazing job of bringing it to life. I've noticed that there a lot of great little touches in some of them. First off, we really wanted to make missions much more team-based. A good player could complete many of the missions in R6 with a single operative. RS missions aren't like that, especially on elite.
Snipers add quite a bit, as do the fact that hostages can move around the map on their own.
They are much more dynamic and therefore, much harder to predict. Spec Ops 2, Private Wars, and the like. You can always learn from the competition, even if all it does it to verify that we're doing the right thing. The grass in Delta Force 2, for example, looks really nice. It made us look closer at how we were doing our vegetation.