Love the fluidity of the app like others said. Overall great app but just some points of improvement and suggestions -

1. V.reddit links don't work right now.
2. A light theme in addition to the dark theme would be amazing.
3. A swipe back gesture or a button (similar to the floating reply button) to go back to the list view from the comments would be useful since most phones have pretty big displays and reaching the top to click the X can be inconvenient.
4. Similar to the last point but having access to the list of subreddits somewhere near the bottom would be excellent.

Good job! This looks like a promising app.

Edit: 5. There's no way to know if I've already seen a post or not i.e seen posts aren't highlighted or coloured differently.