The problem, as i see it, is that it is the wrong kind of engine, in the past there have been two choices for a shooter:
1) The classic FPS engine:
As old as the FPS itself, the FPS engine offers the very best in eye candy and player interaction with the world, thats what they where build for, but it comes at the cost of level design, maps have to be kept small and are connected by hubs, limiting your design choices.
Some can model the outdoors to some degree, others can barely model a town square without struggeling, but regardless, maps made for the classic FPS engine tend to be small and linear by necessity.
2) The "Sandbox" engine:
We got our first glimpse of thease with the likes of OFP and GTA3, expansive and varried worlds are possible here, entire islands and cities can be moddeled, but at a cost, eye-candy is usually much lower here than with the FPS engines, and whats worse, the way you interact with the game world usually feels.. a bit off, the physics just aren't there, things feel clumbsy and disconnected from the world, AI has usually been quite poor, and some of thease engines have really struggled to model indoor sections, its clearly a tradeoff, and plays as such.
This new Tech5 engine is definately of the classic FPS variety, sure it has vehicals and probably more terrain than Source, but all the same it is very much a classic FPS engine, but theres a problem.. lately, we have been seeing hybrid engines, they have been around for a while now, atleast since FarCry, but now they are finally maturing, and with more and better to come, the classic FPS engine nolonger holds much appeal.. why buy a Tech5 license when you can have the Crysis engine? or even UT3 or that engine STALKER uses?