[tinkthank]

I think Sheap is dead on with his excellent summary of Caelum and its weaknesses, to which a large number can be added easily.

One could note that both Man (tuatha) and Van have very very easy access to what Stormbinder calls "PD-killers", only that they are more expensive and much much beefier (and with glamour, yikes). Tien Chi S&A comes to mind too, and standard Tien as well with a pair of super-cheap flying boots. Well tons of nations can fulfill the role of PD-killer with flying boots, actually, but whatever.
I find Caelum to be very strong -- but, like Ermor (which I dont find that strong in MP), fairly inflexible. Strong, but not crying for a nerf; strong, but not bannable from games.