The acting in the first 6 eps of season 4 is just spectacular in my opinion! These are some of the best eps of the series, and everyone does an excellent job from Bruce to Andreas to Wortham Krimmer and Wayne Alexander.
I agree, I love those six episodes with The Hour of the Wolf and Into the Fire being just slightly lower in my book than the middle four (but just by the difference between A and A+). Throw in the last three eps of season three (all A+'s in my book), and the entire season 3 to 4 transition is my favorite "clump" of episodes in the entire series.
The acting, overall, is pretty acceptable to me, and sometimes outstanding, especially from Katsulas as G'Kar and Jurasik as Londo. If there's any acting that is weaker than standard, I'd say it would have to be during the crying scenes.
Crying is probably one of the harder things for an actor to do. Some can do it well (Robin Wright Penn), and some can't (Matt Damon). There is one time, I think in Hour of the Wolf, that Ivanova is doing a little crying, and it doesn't quite come off right. Even when an actor cries convincingly, it can still be slightly annoying. When Delenn cries, as she does a little in her argument with Sheridan in Z'ha'dum, her voice quivers in a way that bugs me just a little.
I can also see how some may not like Wortham Krimmer's acting as the Centauri Emperor, because it is *way* over the top. Oddly enough, I like it. It's consistently over the top and over the top in a good way. He's crazy, so you shouldn't expect him to be even keel. The heirarchy for the throne must have been pretty sucky for them to have to fill Turhan's place with his nephew, and surely Cartagia's insanity was noticeable before taking the thrown. Man, were they desperate. Nonetheless, great character, cool name, impressive performance.
And, Wayne Alexander as Lorien... Perfect.