A totally different type of Gears Game -- not for Single-Player enthusiasts at all. FUN scenario-based Co-Op MP.
The Overrun mode is certainly comparable to "Beast vs Horde", but it really is its own game. It's absolutely all about talking with your team, choosing character classes and positions accordingly, and generally having fun with it.
And the FFA mode feels more like Unreal Tournament than anything since... well, the last Unreal Tournament (but all small maps). Again, lots of non-serious fun.