Both Ghelarn ambushes pretty much wrecked my players, as they failed to notice either of them until they were right on top of the monsters. If I had it focus on attacking specific PCs and dropping them instead of having the Ghelarn overconfidently attack every one within reach with a single tentacle, I would have easily killed a PC in the first encounter, and possibly had a total party wipe in the second... or at least had only maybe one or two heroes limp out to try and get a whole new group. (my PCs were 2nd level and there were five of them, for perspective.) As is, they survived, but were pretty demoralized.
I recommend caution in using the Ghelarn. I think it's a bit nastier than its CR (2 for normal, 3 for advanced,) suggests. Grant you, the same could be said for Hetuath, the Juju Zombie Kasatha Fighter, who did kill a PC and needed to be fled from on the first encounter, but Juju Zombies are nasty and 4 attacks a round are nasty at that level.
Of course, your mileage may vary when it comes to monster difficulty and PC death at early levels. It's possible I'm a tad squeamish.