Chuuls are aquatic aberrations that grab people, then paralyze them with their tentacles. Sadly, they have several issues that make them near-unplayable.
The first is obvious: 11 aberration RHD. This means you're missing out on several points of BAB compared to a full BAB-class. In addition, the high RHD will restrict you in your class choice: you won't even be able to finish many prestige classes!
Then there's the issue that chuuls just aren't that good at their primary role: damage-dealing. 20 strength and large size are good, but not great, especially at this level. Their claws deal little damage and there's no easy way to wield melee weapons for them. Chuuls can't even use their main ability (tentacles) without giving up a full attack!
On the subject of that ability, it's pretty bad. First they need to hit with a claw, then they need to grapple, then hope their subject can't free himself/teleport away in the next round, then give up a full attack to transfer him to their tentacles... and only then does the creature make a saving throw versus paralysis. Oh, and this all assumes their victim can't just ignore the grapples completely (FoM and incorporeality aren't exactly hard to get).
Are there no good sides at all to the chuul? Well, they're decent grapplers and their paralysis attack can be devastating against the right foes. Despite that, -0 LA is enough.