I found they hold up very well. Yes, he doesn't follow the same formula for book after book like so many series do. The main character in the Indian Mutiny one is a long way from a decent, well set up young chap.
For The King's main character is the opposite of a gung-ho into battle, hooraay everything is black and white sort of person.
Knight Crusader himself is a rather modest charming person.
Just occasionally there is something I look at and think that if he were writing today he probably wouldn't have said that - it was mostly in Mohawk Valley, set in pre-Independence America and there are one or two references to Native American characters that weren't in any way horrible, as Welch doesn't do that, it was just something in the phrasing that made me wonder if a Native American might find it offensive. The same for a couple of black characters. I have seen a review where someone didn't like the way he portrayed a few puritan characters who make a relatively brief appearance but not anything objecting to his non-white characters.
Knight Crusader was still paperback price the last time I looked, so you might want to try that before committing to the whole series. Though then again, you can just read the sample courtesy of Amazon and that might be all you need to confirm you still like them.