After a little bit of a wait, Total War: Three Kingdom's biggest DLC so far, Mandate of Heaven, has now made its way to both macOS and Linux. It brings with it over 40 new combat units to fill out your armies, six new warlords with their own unique mechanics, as well as origin stories for some of the most famous characters in the time period.
It's also worth mentioning that unlike the previous DLC, the Mandate of Heaven campaign will seamlessly transition into the main campaign. The various important events, as well as the rise of brand new factions, will all unfold as you progress through the years. So while the campaign map is unlikely to look the same by the end, you should still be able to experience everything Three Kingdoms has to offer.
You can get a pretty decent idea of what the story is about, as well as which characters will play an important role in it, through the original announcement trailer. Have a look, it's quite a pretty one:
As for whether Mandate of Heaven is any good or not, I'd say the answer is a solid yes. It has brought in some much-needed variety to Three Kingdoms, and while I still feel there is a lot more work that needs to be done before Three Kingdoms can rival Warhammer 2, this is a solid step forward. So if you're really into Total War and want to get even more hours out of Three Kingdoms, then I'd say Mandate of Heaven is worth looking into.
Have fun, and if you need a bit more information, you should head on over to Steam. As always, Creative Assembly has done an excellent job highlighting all of the DLC's features.