I like it as a glass cannon option. If I want a glass cannon for an encounter, this is a good one. If I don't, I use a different creature. I'd be disappointed if there weren't some glass cannons in the MM, just as I'd be disappointed if there weren't tanks, snipers, area controllers, and whatever else I needed for a scene.
Interestingly, I've found that the best creatures to scare and fascinate my group are the seemingly "unfair" ones. My players yawn at giants and most demons, and even most dragons. They know that those creatures are largely about damage expressions. There are ways to mitigate lots of attacks rolls or high incoming damage. The things that
scare my players are the creatures that kill you in ways other than pure damage. And here's the weird thing: the things that scare them are also the things that get them excited, and create the most memorable stories.
Medusae are scary (petrification). Wraiths are scary (max hp reduction or level draining, depending on edition). Mind flayers are scary (whether it be domination, mind blast or brain-boring). And intellect devourers...? Intellect devourers will be very scary, especially for that 8-Intelligence / highest-hp-in-the-party / resistance-to-all-weapon-damage barbarian who laughs off waves of incoming ogres. I need something in my toolkit for that guy. I'm not going to kill him with it arbitrarily, but I certainly want to be able to worry him.
