It's OK on desktop but not great. I always accidentally hide or flag posts I don't mean to. It's impossible to keep track of discussion threads and replies. The threading is pretty unclear.
On mobile it's just terrible. The links are too small and too small together. The reply box is small and you can't drag it bigger. The contrast ratio of light gray on beige is really bad for my eyes, especially at night in dim light.
I actually strongly dislike the UI of this site, but there are so many old timers who like it that way that a redesign would probably kill it like it did for Slashdot and Digg.
There are some apps that do a better job, but I haven't found one that works well with reply tracking yet.
Making an alternative frontend has been on my to do list forever now, but I imagine it would be a niche (and definitely controversial) take that most of the old timers would hate.