I hated Reveal.js until I realized that I could press Space to advance, and Shift-Space to move backwards, and it will just Do The Right Thing.

Can you go down? Space will go down. Otherwise, Space will go to the right. It re-linearizes the presentation, while still preserving the 2D layout for quick navigation between major topics.

I would have never said that, but now that I've come across it a few times, I think it's great – easy to get an overview of high level topics and dig into those that are interesting. Definitely not very discoverable, but pretty useful.

For those who are confused: Hit the down arrow to go thru the slides, when you get to the end of one, hit the right arrow to go to the next section, then rinse and repeat.

Just hitting right will show the you the headers for each section. Right jumps from section to section

Hitting down goes slide to slide.

I've used this aspect of Reveal to present an overview of my talk at the beginning: "We're going to talk about X, Y, and Z. Okay, so X..."

Believe it or not, on a phone I found it to be a completely reasonable interface.

It's actually all three. I like the format.