The Immortal Empires megacampaign for Total War: Warhammer 3 was long-awaited, thanks to the popularity of its predecessor, the Mortal Empires campaign for Total War: Warhammer 2, and to Warhammer 3's default Realm of Chaos campaign being a bit underwhelming on the second playthrough. Since Immortal Empires came out in beta, Warhammer 3's player count on Steam has shot up like a Doom Diver.
Warhammer 3's peak concurrent player count on Steam was 166,754 when it launched on February 17. That quickly dropped, and for the last three months it's been hovering between 8,000 and 12,000 players. With the beta release of Immortal Empires on August 23 it zoomed back up, hitting 119,166 that day. It's remained high since then, and today reached 103,952, putting it at #11 on Steam's list of top games by current player count just behind Rust.
It probably helps that there's a Steam sale on the series at the moment, with the first two Total Wars Warhammerses in a bundle for 75% off. (You need all three base games to play Immortal Empires.)
Our own Fraser Brown got into the beta early and played a campaign, concluding that, "It should be too big, too unwieldy, and it's certainly very messy and hard to wrap your head around—there must be a limit to the number of unique faction mechanics the human brain can juggle—but it's all just brilliant." Sean Martin has been playing Immortal Empires as well, and managed to break the campaign with a Black Ark super fleet, though he certainly had fun doing it.
With 278 factions and 86 playable legendary lords to choose from, I suspect it'll be a while before players get tired of Immortal Empires. It adds Realm of Chaos campaign villain Be'Lakor as a playable lord with his own faction, and gives dedicated factions to existing lords Grombrindal, Helman Ghorst, Volkmar the Grim, Sigvald the Magnificent, and Kholek Suneater. Sea lanes, which let you move armies between distant lands, are another addition, as are randomized endgame apocalypses that throw an extra challenge your way just as you're getting to the point where victory seems inevitable. If you feel up to it, you can even turn them all on at once in Ultimate Crisis Mode.
