Geez, late to the party and all the good critique is already taken...
1. I agree with the comments about a tighter crop working on this one, but I also like it as-is; I get sort of a 'Secret Garden'feeling from it. I do think though that the foliage could use a little brightening. Perhaps some additional levels/curves adjustments?
2. I think a slightly different shooting position to eliminate that little patch of bright, white sky, upper-left. My eye keeps going straight there. This one definitely needs leveling and a perspective correction wouldn't go amiss either.
3. Sorry, nothing here. To be honest I had to look at it three times before I even saw the cow's eye! The idea was good, but the execution should have been more side-on to eliminate all of the distracting lines, especialy the fence and the dark fur in the background.
4. Again, as with the cow, a little too 'head on' and not enough profile for my taste. As well, this is a situation where you really want to try and use selective focus to make the subject stand out from the background. Also, be sure that you don't lose little bits of the subject, in this case the feet. If you need to crop body parts, whether human or animal, the general rule is be bold; this looks more like you just weren't paying quite enough attention.
Just my $00.02 worth - your mileage may vary.
~John