Not much wrong with it at all, it's nicely exposed, good colors, nice depth of field. It would have been a better pic had you been able to see the face and eyes properly, maybe waiting for it to turn but rather take a shot of it looking away and hope to get a better shot than not take one at all in the hop of getting a better pic.
you might want to crop it a bit so the animal is a it bigger in the frame if you can;t get any closer to it
i think it's pretty good and squirrels make great subjects
now then as a photo it's quite interesting the lighting and long shadows adds mood to the scene and there's a squirrel to compliment the scenery
overall it's a good photo but some would say the squirrel is too small in the photo it's looking in the wrong direction etc.. ( pretty much what cathus has already mentioned ) but it doesn't have to be all about the subject
like i said squirrels make great subjects as they can be quite tame and a few peanuts wouldn't go amiss to attract them to where you want the photograph
now ( winter ) is probably the best time as well they will have there full winter coats and will be looking there best they can look quite scraggy during the summer
i think cathus covered all the bases regarding how you want the squirrel to look in regards to posture
make sure the eye is in focus and there's a little catchlight within the eye so it doesn't look dead this is quite important for bird wildlife too
sometimes it's a good idea to pay attention to the background and try and isolate the subject trying to eliminate clutter or branches behind the subject so it doesn't look like there's a branch growing out of it back , head etc..
it's a good idea to leave a little space in front of the subject too rather than cropping too close but i think thats down to taste
most of my comments have already been said. What I would like to add is that it's great to see you 'get doen low', taking it from squirrel level. You have obviously grasped depth of field, and are nearly there with the rule of thirds, which of course can and should in some instances, be broken.
I have spend a lot of November taking squirrel photos in our local cemetary and had a great time.
The best photo's are always taken by someone else