[Endoperez]

No effective counter against what? Masses of Caelian Archers backed up by few mages, masses of Caelian Infantry backed by some mages or lots of seraphs backed up by some archers/infantry?

Caelum's archers are quite good, but still die quickly if anything gets next to them. And they eat a lot. Fast Caelian infanty is quite bad, too. And the good ones are not only expensive but slightly slower as well. And the "lighter complexion" of Caelians that enables flight also makes them weaker than their human counterparts. I haven't tried them in MP, but I quess they will be quickly decimated if your enemy manages to surprise you in any way. And the mages are excellent, as they should.

I can see mountains blocking flyers, but I don't think swamps or forests would be much of a hinderance to them. Maybe in Dom3...