Why is this book regarded as a classic? I enjoyed reading it but I don't think there's any depth to the story...

Depending on how you were brought up, you might not really get the book on an emotional level.
It's about becoming an adult and accepting the (shitty) world with all its nonsense.

I hated it the first time I read it. Hated Holden, hated Salinger for writing it.

When I took another look at it later, I began to realize the brilliance of what he did. Salinger had undiagnosed PTSD. Holden is telling the story from some sort of mental institution. To maintain that voice so consistently for over 200 pages was quite a feat. It resonated with an entire generation.

This.
Not that guy, but if you're just getting into reading I'd recommend Slaughterhouse 5.
It's an easy to read classic that deals with emotional issues in an interesting way, like catcher does. It's also funny.
Regarded as kinda pleb tier around here, but only because it's easy.

classics? well some of my personal favourites are:

rudin by ivan turgenev
kristin lavransdatter by sigrid undset
tristam shandy by lawrence sterne
the female quixote by charlotte lennox
confessions of a justified sinner - james hogg
two series ladies by jane bowles
the sorrows of young werther by goethe

but in terms of books you "should" read then moby dick by herman melville and don quixote (raffel's translation) by cervantes would be the best place to start.

oh and add hamlet by william shakespeare in the "should" pile.

slaughterhouse 5 is great and definitely not pleb tier. elitism is stupid. literature is all about taste and if you're not reading things you like for fun then its a waste of literature.

Alright thanks for the suggestions. I'm starting to get so much books on my want-to-read list that might have to get a job to afford them all.

It's regarded as a classic because it was written a little while ago and it's ideas are still more than valid today.
Pretty much the main thing that makes any older book a classic.

Of mice and men, Steinbeck

If you figure it out, please let me know. I always ask others, and they say that I just don't get it without actually explaining it (or explaining it well).