I'm currently 3 hours and 32 turns into my Slaanesh campaign - so far, I really like it. The campaign is much better than the Vortex campaign in TW:W2 - it seems more focused, as the objectives are clear and there are a ton of missions to usher you towards your goals. My performance is very solid, too - I haven't encountered any bugs at all, end turn times are very quick, and my FPS at 3440x1440 on Ultra settings is easily as high (or higher) than what I currently get on TW:W2 (running on a 3080 Ti).
There are definitely a lot of siege battles, but most of mine have been in the new minor settlement maps rather than the walled settlements that require siege equipment. The new map styles are actually pretty fun, if a little on the video-gamey side with the magic capture points and such. Also, it feels a lot easier to draw in enemies for ambushes and field battles now - using a weak decoy army, I've been able to lure Skarbrand and his Khorne forces into multiple battles.
Of course, there are things I don't care for - for example, the Slaanesh tech tree is very underwhelming and clunky. There are 6 major tech nodes, each with 6 techs to research in each node, each taking 6 turns to research as 6 is the number of Slaanesh. You need to research the first 5 techs to unlock the final tech in each node, but they're often weak, redundant, or very situational. I think one of my first projects when the new Rusted Pack File Manager is updated and the Steam Workshop opens will be to revamp their tech tree with a Sexy Slaanesh Science mod to make it feel more rewarding.