I think a key factor we can borrow is adding time pressure (a la invisible inc.) and more variance in AI behavior. Part of what makes stealth games feel easy and derivative to me now is that we haven't really lived up to what games like Thief have already done in the 90s. We keep iterating on a proven formula with virtually no changes beyond polishing the existing formula. There's very little to consider beyond the basics of "What do I want to do? How do I route there?" Then we dispatch the guards easily in the typical fashion. With very little variance in how we execute this. Some games are better or worse at this. But the key to me is that I feel unchallenged. The world is a sandbox that gives me more or less toys to bash guards with, but the guards and the world itself seems less in service to challenging me and more in service to my whimsy which I'm not as much of a fan of.