For me, I liked the ability to swipe left and right between subreddits (the order on which you could configure), you could also swipe between posts. It’s also open source and pretty customisable. Unfortunately it’s not been updated in over a year.

I can’t speak for everyone, but I really enjoyed the “get out of your way” style the app has. I also really liked that you had to slide to upvote/downvote on posts instead of having static buttons you can accidentally press. It also had a decent system for switching between multiple accounts. Finally, it’s all open source so one could fork it and customize it if they wanted to.

I like it because I like the feel of the old Material v1 theme (it seems the most functional to me), and Slide takes it and uses it to its limits.

The concept of swiping was used everywhere. Makes it quick and easy to use. You could just swipe right to close a thread, or the video/image. No need to use the back button, or reach for the tiny X in the corner.

And the seamless galley mode was awesome. Very unique (only found it quite similar in Joey).

Custom color-coding of subs was nice when you scrolled so far you forgot where you were.

I really like it has buttons to jump to previous/next parent comment. It made skimming top comments a breeze.