I've played and run this module. Overall, Mind Flayers are always fun. It's a little odd to have Gith allied to a Mind Flayer, even a rogue one, but I can work with it. I think I've had it stay around its 2 hour design target, though usually a little over (having a party whose APL is below the target probably makes it run long).
This is a nicely contained module to run since, aside from introduction and cleanup, it's a four room dungeon plus the boss room. Each of the rooms has its own interesting nature. Note that I say interesting rather than particularly deadly. If the dice are particularly unlucky, particularly on saving throws and party composition, this module can turn super deadly in a couple of places, but without bad luck it's flavourful while still within a party's capabilities (disclaimer: I've only played and run this module with Very Weak / Weak parties; I'm certain that if I threw the Very Strong version of this module against a Very Weak party, it would be deadly). I have not yet seen the boss get to his flee condition, because he has always been defeated before it can take place.
The puzzle / trap room was fun to run. I suggest being ready for players to try all sorts of things to avoid their character triggering the trap (use Mage Hands, Unseen Servants, 10' poles, etc.). Since the damage is most psychic, I explained that it followed the chain of intent back to the PC triggering the tiles to be revealed. Side note: Paladin auras can really take the sting out of that room.
Oh, right: I kept nearly forgetting (or outright forgetting) about the faerzress wild surges; they added some hilarity to the table, though they can slow things down a bit (I keep a printed copy of the wild surge table with my notes for the module).
Update: I played this module one more time and the whole party failed its Int save to the Mind Blast. Being stunned certainly made it feel more threatening than the previous two runs. It took until the second round for two of the Monks to make their Int saves, at which point they stunned and totally rolled the enemies starting at the top of round three (which was good, because the other 3 PCs failed their saves for the full 1 minute duration).