Uninteresting means failing to hold anybody's attention. Nothing wrong with it, and nothing to say about it either.
It is a flat and rather cold judgement, which is why it is more damning than boring in some contexts, since boring at least provokes a reaction. It describes things, subjects and, unkindly, people. British understatement uses not uninteresting to mean quite interesting, which is a double negative doing real work. Its opposite is interesting, and the adverb uninterestingly is almost never used.
1adjectiveuninterestingNot interesting or able to hold attention.
“The second half was frankly uninteresting.”
From un- + interesting.
Etymology from Wiktionary, CC BY-SA