The Gauls seem to have some good bonuses, but I think they are a little "all over the place" and I really think the "no adjacency bonuses" from districts is kind of harsh, as well as tying so much of their power to mines, strategic resources and quarries.
That sounds to me like a rather inconsistent civ, if you happen to have few strategic resources and/or hills around, and makes you definitely want to set "World Age: New" for each game to secure more mining opportunities.
There's also the issue with tying lump culture to unit production.
Early on that sounds great, but generally when I do domination I find that by the medieval/renaissance era, I mostly stop producing units alltogether and just upgrade those I have or buy new ones for gold or faith.
At least with Gorgo, her culture bonus is tied to unit kills so it keeps being relevant even if it does fall off in strength.
That being said, what immediately struck me is that Gaul might be able pull off a hyper-aggressive ancient era rush involving mass unit production in order to rush Agoge (for even faster unit production) into Oligarchy for fast additional combat strength, where all the produced units tie in nicely adjacent to each other for even more combat strength.
I have obviously not tested this to see how the timings work out, but it might be worth a shot.
If it does, Gaul should be right up there with Sumeria, Nubia and Aztecs for their early rushing potential.