I have yet to run Shadowdark, but it seems like a perfect way to introduce D&D 5E players an oldschool dungeon craw campaign. There's familiar mechanics (dis/advantage), the old percentile Thief skill tables are gone, and DCC-style "roll to cast" seems like it'd be more palatable for folks used to attack Cantrips and ample spell slots. Plus, Kelsey Dionne is a fantastic adventure writer, so we're all but guaranteed years of top-shelf modules.
Yup, unified resolution mechanics tend to be easier for new players to grasp. (I suppose a good comparison would be if Call of Cthulhu had you bust out a d20 to resolve breaking and entering.)
Shadowdark (like White Box: FMAG) replaced the d100 thief skills table with a simple, "Roll advantage on Thief type ability checks." It's a personal preference thing, but I like it.
@copacetic I have been planning to run Shadowdark in my in-person home group (currently running CY_BORG) when the physical books arrive. I didn't want to wait, so I've been prepping Shadowdark for online play in FoundryVTT which has pretty good support. The Shadowdark discord ( https://discord.gg/thearcanelibrary ) has a thread on using SD in Foundry with tons of resources and super nice helpful people.
Funny, just finished scarlet citadel (pretty unsatisfied with the 5e dungeon crawl experience) and currently running a few shadowdark one shots as a result. I love the simplicity, clarity and conciseness of it compared to 5e and the armada of retroclones at the other end of the spectrum. Oh yeah and the speed of combat might be the best thing overall.