Was his teachings Buddhists in nature?
This is a quote from the page you referenced ...
Krishnamurti said: "I maintain that Truth is a pathless land, and you cannot approach it by any path whatsoever, by any religion, by any sect."
... so, according to him, accoding to that, maybe not (not in name).
From the same page ...
Krishnamurti was raised within the Theosophical Society to become an incarnation of Maitreya, the messianic Buddha.
... so he was presumably (I don't know) exposed to some kind[s] of Buddhist doctrine.
Do any Buddhist teachers or philosophers opine about him? If yes, in what ways?
Well I don't know about him in particular.
This answer says that the Theosophists (I think these were an early 20th-century European group) were trying to consolidate all religions into one -- to say that all religions were essentially the same or One in some way.
I think I've seen some people (who would call themselves themselves Buddhist) disagree with that doctrine, and disparage the Theosophists, so ...
See also e.g. this answer -- someone leaving the "Theosophical" society to found a "Buddhist" society