Currently debating with myself and talking with potential players about a summer game of either Demon: The Fallen or Demon: The Descent.
Fallen is more straightforward in both setting and rules, and I’ve never had a chance to do anything with it in almost fifteen years. But Descent is more complicated in interesting ways, and lets me do spies...
The Venn diagram of material likely to feature in both is really pretty small despite both being games about demons passing for human in the present, and I could swipe a few ideas from one for the other. They both favour differing approaches above all. Fallen PCs have much less reason to be subtle than Descent ones, for one obvious example. For instance, both Unchained and Fallen have an option to drop the mask and Hulk out, but it’s much more of a last resort for the Unchained, because it (a) sets off every demon-detector the Angels have and (b) destroys that cover. Various other decisions encourages sneakiness rather than might.
I’m probably dwelling on the differences. The Fallen can be subtle, as future Descent creator and co-developer Rose Bailey’s Fallen game Strange As Angels demonstrates, and there’s a Translation Guide for switching or merging the two. A version of Descent without the biotech wouldn’t even need it, for instance - call the God-Machine the Demiurge and you’re halfway there.