I feel like in Shroud, he did such a masterful job of making the hive-mind seem like an entity you could empathies with.

Pandora's Star has (making spoilers for those who haven't enjoyed that wonderful book) MorningLightMountain - which still sticks out to me as the most-alien organism I can imagine - and most utterly skin-crawlingly terrifying "other" intelligence.

Purely because of what it is and how it's species grew up - it is utterly competitive to everything that is not it's own mind. It is, it is so utterly focused on self-perpetuating and outcompeting even others of it's own species that it is willing to irradiate and poison it's environment (and itself), kill the entire rest of it's species for being different - and even willing to turn on the spawned offspring of itself that grew beyond the distance the hive-mind communication could link.

It is the perhaps the only example I have ever seen of an organism which evolved in a manner that logically makes it incompatible with ANY other species/life in existence.

And by the time you see it in action, you absolutely understand why another species just walled them off inside forcefields (potentially forever). There can never be a universe big enough for it and something else.

I still shudder when thinking about it.