I have returned! (But I won't stay for long)
The celt's plot is a bit more realistic. With the romans, the plot relies somehow on the stupidity of your comrades,(save the skull) else the game would be way shorter, and so Jeff had to make such a plot.
Also there's a feeling in the romans plot which makes you feel like having to do anythingyour leader wants you to do, what's of course right, you're roman soldiers, but I don't like the feeling.