I didn't mind the Celtic stuff. I mean, you get down to it, the British Isles are rooted firmly in Celtic traditions -- Anglos and Saxons and Romans and Norse, etc. are all newcomers. Any pre-5th-World stuff would carry forward into Celtic traditions, so it isn't that I mind.
It's the problem of 'bigger and better', on top of the issues of 'okay, so if the players don't want to go this way, shoot them in the head and bury them on the heath'. Imago is the worst I've ever read through or played through; I haven't read Celtic Double-Cross through, so I don't know if it's actually worse. But in Imago, if you don't go along with the railroading, you get ***ked six ways from Sunday, and he does this to you at every turn.
For the sourcebooks (TNO and London), it's like they decided that everything there had to be better than anywhere else in the world. The mages were more powerful and more advanced. The disasters were bigger and deadlier and more destructive. There are (count 'em, at least 3) more Great Dragons per square mile. Never mind the fact that there are SO many places that are at least, if not more, historied than those comparatively small islands in the North Atlantic...
Just makes me want to shoot them both.