The technical issues at launch are kinda inconsistent. Some people are reporting that they're getting better performance than WH2, some are saying it's significantly worse on similar settings. I'm in the latter camp; I could run WH2's campaign map at almost a steady 60 fps on High settings, but in WH3 with lower settings, I'm struggling to stay near 40 fps, sometimes dipping below 30. Battles run far better--a stable 60 all the time.
A lot of people are mystified on why the performance has taken a nosedive; those who got pre-release copies were reporting that the game ran as well as, or better than WH2 on the campaign map, and suddenly that's changed for them after launch. Many have pointed fingers at the inclusion of Denuvo in the release version of the game, but it's uncertain. All we know is, between pre-release and release, something got screwed up for many users.
As for the main campaign, I've found it much slower--not necessarily bad--and a bit annoying. It feels like I'm heavily discouraged from doing the usual Warhammer thing of fighting wars and taking territories, because the more provinces I take the more chaos portals I have to play tag with. The most effective path to winning seems to be making friends with as many neighbors as possible to avoid war, then turtling with a single doomstack and casually waltzing into the chaos realms to claim souls and win the game.
Different isn't necessarily bad, but this new campaign feels like it's unnecessarily restrictive and generally not very Warhammer-y. I'll probably have to wait for Mortal Empires to be ported over before I can start having some real fun.