The basic idea of mixing two Asterix stories together was not too bad at all: the Romans were a bit too pale and one-dimensional in the original big-fight story and the druid's absence and the resulting threat to the village was underexplained in the original soothsayer story.
However, the result sacrifices most of the satire of either story, aiming at a young kids market (which really isn't the traditional Asterix audience). But it is not just the story - also the animation moved a couple of furlongs towards Disney territory, especially the musical number made me cringe. How can the villagers dance to this bard's singing? It is supposed be painfully abysmal! A nauseatingly bad musical number would have been fine, but the film makers simply didn't dare.
I also could not warm to the English voices. While Brian Blessed put some oomph into his character, he overdoes it, as usual. An example of a scene which required cool understatement was when then the centurio instructed his messenger to Caesar. Blessed speaks it with too much excitement, though 70% of the blame has to go towards the director as the animation is similarly hyperactive at this point.
The English title of the film still sticks with "big fight" which is misleading as the actual fight (the one between Gallic chiefs) is not in the film.