I found it pretty boring, to be honest. Felt like an excuse for the author to show off how smart they thought they were, without really any skill at characterization or meaningful plot.
And like, I'm not a writing snob. I read fanfic by amateur authors. But HPMOR just doesn't do much of anything interesting.
There's lots of valid critiques of HPMOR (I recently reread it and the early chapters are painfully obnoxious), but I think "no meaningful plot" and "doesn't do anything interesting" are objectively false. It has like a dozen interacting plotlines, and is massively different from any other HP fanfic and most media in general. It is popular for a reason. If you dropped it early, I'd encourage you to try again.
And like, I'm not a writing snob. I read fanfic by amateur authors. But HPMOR just doesn't do much of anything interesting.