It looks like this will also follow the template of the Spelljammer books, with some player options, setting information, and DM facing content (adventure & creature statblocks).
...i think planescape + planebreaker will be the way to go for fifth edition, similarly to spelljammer + the ætherial expanse, but of course there're also always DM's guild reprints to flesh out TSR-specific setting lore...
...i did the math last week with an imaginary shopping cart and calculated that we can get the entire corpus of second-edition planescape material in (re)print for about $300: tempting, albeit pricey...
Having played Planescape: Torment for the first time back in 2018, I've been wanting to run a game based in Sigil since then. Currently resisting the urge to pre-order rn, ugh.
Resist the urge to preorder. The book isn't going to give you enough information about Sigil to run anything. If you want to spend your money well go into the DM's Guild and pick up the 2nd edition PDFs of "The Cage" and the planescape boxed set instead.
Is there any down side to wait for reviews of the books contents?
While this theme heavily Interests me, the last Releases of WotC have Not been too great in quality
Looks like no new subclasses based on the description. Nor are there any races listed (what's the new term? ancestry? Species?) so this feels lacking in the character options as well. Maybe that bodes well for the setting materials?
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