Rule Britannia is pretty damn good. It takes my favourite Kingdoms campaign and makes it even better. However, there is one major fault. Contrary to what Braveheart would have you to believe, Scotland wasn't entirely composed of Highlanders. The Highlander units that the make up the entire Scottish faction are historically inaccurate.
Now, this IS, as stated, just making Britannia better, but it would have been very nice to see some historical accuracy.