First off well done getting the shot - wildlife is never easy to capture! The shot also appears well exposde - though its slightly darker overall, there is evidence that the lighting on the grasses in the background might have cause overexosure in them had ou gone brighter - though there is a little possible (web compression makes it hard to tell) overexposure in these areas its acceptable
Personally I think the problem with the shot is that the beaver is not standing out from his surroundings or background - infact he blends very well into his surroundings. This is very good for him, but not so good for you since it means that the shot appears cluttered and finding the point of interest is difficult. *unless of course, the shot is displaying an example of beaver camoflage
Personally I think there are several options that you can try to improve the shot:
1) get closer - either yourself, the beaver or get a longer lens

Unfortuatly there is never a lens long enough for wildlife (its always just that little bit further off). A tigher crop to the shot would help foucs the attention on the subject
2) better lighting - perhapse try and get the light to fall not on the background, but more onto the beaver. Evening or dawn lighting would work very well for this and not introduce the problems of shooting at the brighter parts of the day with overexposed highlights. ITs not something that you can directly change, though something to consider when shooting.