I think it looks good, though as for being realistic... my initial though is that some facial features are either way under or over proportion. The nose and lips specifically stand out a bit much, as if it was a fishface photo effect. The nostrils on the nose seem unnaturally symmetrical and not in proportion to the rest of the nose. The jaws stand out a bit much right under the ears, and there seems to be a sliver of left-over color here.
Otherwise the shapes are nicely defined, overall the skin has a very smooth surface texture that reminds me of claymation. It looks great, but I think it lacks realism in how there are no defects, no oddities on the skin other than shade or shape, lack of texture maybe. That and the proportions. If you'd want to draw caricatures then this style is definitely worth building on though!
But back to realism... the glow on the adams apple is a bit much, the shade under the lower lip makes it seem like the jawbone is misaligned or something, near the shirt it's light all the way around, and near the hair there's a sliver of light where there could be shadow. It looks great otherwise, and the way you mix colors on the skin rather than use the same tone for all of them is great. The clothing texture looks very realistic, just missing some kind of texture around the collar. Hair looks great, albeit a bit overly neat near the hairline, eyebrows seem too solid, and the eyes have strangely beige whites. You could work on making the pupils a bit more lifelike as well, but that's definitely the hardest part.
Overall it looks good, but since you asked for critique... I'm trying to find all the flaws I can. :) it's a great start, looking forward to future work!
-cd-