The nice thing about drawing Cthulhu is you can never draw him the same way twice. Lovecraft’s description is specific enough to give you something to work with (octopus, dragon, bipedal, scaly wings) and yet vague enough to leave lots of imagination space. I recently found this gallery page with 101 great Cthulhu images.
If I had one complaint about drawing Cthulhu, though, it’s that he’s so humanoid (in most interpretations). It’s hard to get away from the basic skeletal structure/body shape of a human being, with the legs this way, the shoulders this way, the hands this way… but since he’s an alien from another planet, and not just a demon or something, technically all his joints and limbs should be arranged in a totally different fashion that just happens to resemble a human being, if at all. But this kind of intricate musculo-skeletal rearrangement (assuming that Cthulhu has a skeleton) is hard to do, and even when artists do come up with really alien body-shapes (like some of the designs in Avatar), often these new shapes distract from the creature’s effect rather than adding to it… leaving me thinking “gosh! that monster moves like a metronome!” or “gosh! that has the body shape of a paper clip!” rather than the more appropriate “OMG~!! THAT MONSTER IS CHASING THE PROTAGONIST!” In short, it’s challenging to draw him so that he doesn’t look like a guy in a Toho rubber monster suit. This drawing doesn’t entirely get away from that, but I liked it.