1. Hints - Players love being able to access hints, and when they're not available, frustration sets in. Not only do games need to have hints, but as we've learned, they need to have really good ones! Ideally, players don't use them, but this is a great fallback option. Tiered hints are really appreciated so players don't get the answer all at once. This is one thing we love about Society of Curiosities' games... lots of slowly progressing hints!
2. Layers - Players love combining different layers of information to feel smart; ourselves included! This is where the puzzling comes in. If you step back and think of it, it's kind of mean that the puzzle designer wouldn't just give it to you straight, but that's kind of the point! Can you "connect the dots" so to speak. And a good puzzle design will connect the dots in just the right way, leaving you feeling accomplished. We really like Hinks Gazette by Bluefish Games for this reason.
3. Use of the design - A great escape game makes use of its environment. The design of each item is both beautiful and functional! A great design will incorporate puzzle elements into throughout. I can remember one escape room I did that stumped me, they had a design in the stonework (it was Mayan themed) along the top of the room. It was subtle and high up so you didn't think to look there, but it was revealing a message as well as contributing to the theme. For this reason, we like Curious Correspondence Club.
4. Use of the body - it's one thing to crack a code in 2-D, but it's quite another to get your hands involved: cutting, folding, taping, etc. We love escape rooms for this reason because they are whole-body experience. It makes me think of DaVinci who talked about "corporalita" or the process of learning when the whole body is engaged. We believe there's a lot of good that comes from working with your hands and moving your body! But don't take our word for it... play an episode of Escape Mail (especially Episode 3!) and find out for yourself.