Apparently, this blueish lobster lad is pathfinder's official glabrezu picture. It looks more like a weirdly-shaped tropical crustacean than an awe-inspiring demon to me, to be honest.
Glabrezu are enormous: at Huge size they're even taller than balors. Their strength and constitution are consequently high too, with both in the low 30s. Other stats rank from average (10) to very good (20). They possess two pincer attacks, a bite attack and two claw attacks. Given the humanoid nature of their clawed hands, I'd say they should be able to wield weapons, but I wasn't able to find any confirmation of this.
What can a glabrezu do? Their melee ability is definitely not bad, even when you have to use a mouthpick weapon. Their continuous True Seeing is the equivalent of a 75000 GP magic item, and while mostly obsolute or attainable through other ways, their energy resistances and immunities are valuable too.
Like most other tanar'ri, glabrezu have lots of spell-like abilities. These vary in usefulness from almost zero (Unholy Blight) to useful (Mirror Image, Greater Teleport, Power Word Stun) to potentially encounter-ending (Reverse Gravity). Glabrezu can also summon a horde of dretches or 1-2 vrocks, which I suppose can be useful (please roll me 23 saving throws against Stinking Cloud).
Perhaps the glabrezu's most powerful ability: Wish. Every month, glabrezu can grant a wish to a mortal humanoid (such as your adventuring companions). It should be noted that this is a SLA, and therefore requires no resource expenditure on your part. As this is obviously broken beyond belief, it will not be considered when assigning the creature its LA.
Taking all these things into account, what is an appropriate LA? With SLA's that outclass a warlock, great martial ability and the various permanent resistances or abilities, combined with the fact that your RHD don't hurt that bad, +2 seems a minimum here.