Can't say I didn't expect this. Iberia needed an additional faction to make things interesting and Celtiberians were the obvious choice here. The question is who is next. From a purely gameplay perspective, I think that we need at least one more faction in Eastern Europe (maybe an another Dacian faction?). Besides that, an additional Gallic faction would be nice. The Belgae would fit nicely here.

As always, I oppose the introduction of Syracuse as a major faction for gameplay reasons - they would be dead within the first 10-15 years and they wouldn't even last that long if the player was playing Carthage or Rome. Syracuse can be modded in after EB2 is released (at the cost of, let's say, Saba), but it shouldn't be included in EB2 Vanilla.

I'm not sure about Great Britain - an another faction there would be nice, but only if the region wasn't so isolated in every game. How is the naval AI in MTW2? Does it make naval invasions? A land bridge between continental Europe and England would be lame...