An unseemly high rating for a 16 page book, I suppose.
On the other hand, are you rating from the bottom up, or the top down? 16 pages isn't much room to lose even a single star if using the latter.
Or is it the middle-out, which makes me think of the season one finale of HBO's "Silicon Valley", which I saw last night. (Tip-to-Tip efficiency!)
I suppose it comes down to three feeling far too low for this little book, a lovely and creepy look at a fictional Canadian species of "deer". Five seems a bit much to rank amongst Joyce, Woolf, and Shakespeare. At 16 pages, I'd suggest it's hard to be much better, and quite possible to be much worse.
The art is intense and well crafted, though not in a style you'll find pushing any of your visual boundaries unless you're unfamiliar with the genre. Again, it's value is in the lent intensity it grants to the restrained text, which really is the great technique that graphic art has over text, to say one thing whilst visually doing something a little different. But by now I'm either preaching to a choir, or at the backs of the escaping man on the street. It's his loss, he who fails to enjoy this genre.
Spotting Deer is a tiny and very worthy contribution to the form, and well worth what vanishingly little time it takes to ingest. You've no excuse.