Here's what the composer of Boudicca's themes, Michael Curran has to say about it. I asked him what of people comments that it's not "Celtic" enough.
I am happy that you like the Boudicca Theme music. It is one of my favorites. "The Lass of Aughrim" has been a favorite of mine for many years every since I first heard it in John Huston's film "The Dead" from the short story by James Joyce in his 1914 collection "Dubliners". I believe that Joyce references the tune and Huston included it at the very end of the film.
http://www.youtube.com/watch?v=I1CP5Lz2iHE It is among my favorite scenes in film history.
"The Lass of Aughrim" is most commonly known as an Irish tune, but as I began to research it, I discovered that it had Scottish roots. Many early folk songs of England, Scotland, Wales, and America had a rather intertwined history and evolution. The fact that it had Scottish roots and was related to the tune "Lord Gregory", I thought that I had enough of a connection there to use it as the Boudicca Theme.
I do read the Civ forums regularly and am aware of the comments or type of comments you mention. As to a complaint that it is not "Celtic" enough or that it should have been more like Civ4's Celtic Theme, I would say that the design of Civilization V was very different than that of Civilization IV in regard to the design of the soundtrack and the varied use of the Leader Music in the game. Early in the project, we met with the design leads and determined that we wanted "Cinematic Orchestral" as a style. As for how the "non-western" or "non-classical" music was to be treated, we tried to evoke ethnicity much the way a movie composer would by including ethnic themes and ethnic instruments into the "cinematic orchestral" style of composing. The Civ IV Celtic theme by contrast was written to sound like more traditional ethnic music of the region - or more specifically, what most people would expect that to sound like. While beautifully composed and rendered by Mark Cromer, the style choice was a product of the musical design of Civ4. You can read more of my thoughts about the musical design of Civ5 in articles and interviews I have posted on my website
http://www.michaelcurran.net/esteem.html As to the comment about the lack of bagpipes in the war theme, I would say to go back and listen again. Bagpipes are featured prominently although are doubled along with the orchestra brass. Perhaps that is why it may have gone unnoticed by some.
Thank you for your interest in my Civilization music. Keep listening!
Michael