what's gaussian noise look like?
Yes it is. However, unlike real AWGN which comes mostly from thermal agitation in electronics, matlab's noise is not purely random, this might be the cause of you seeing a deterministic pattern. But this pseudo-random noise is usually random enough to approximate real life noise

If you want to assess the noise "randomness", plot an intensity histogram of In-I, with In being the noised image and I the original image (you are subtracting the deterministic part and keeping the random part).