I won't spend too long on the exposure since that's been the focus of the thread so far. I will add that, except for the blown highlights on the petals in #3, the exposure doesn't seem egregiously high to me (at least on this monitor). They may be a bit bright, but unless you're losing detail, slight over/underexposure can be a stylistic decision. That doesn't mean you blindly expose to the right, but it doesn't mean you can never go a bit bright or dark.
Now, on to individual C&C...
1) I like the subject in that there's character and texture to the window and walls. As has been mentioned, you get a slap on the wrist for cutting off the bottom of the window. I appreciate that you used portrait orientation for the tall skinny window. In this instance I personally think that landscape orientation would have worked better, to get more of the wall into the shot. That would put the window in context - for example, why is the wall different on one side of the window than the other? Landscape also would have given you space to move the window off center, I think following the rule of thirds would have helped here.
2) My favorite shot of the set. Interesting subject - great texture, and nice juxtaposition of the man-made screw standing alone in the dirt. Great DoF and composition. The lighting is a bit flat - I'm sure that's a function of the overcast day, but I'd suggest revisiting this location and trying this shot again with various light situations (clear morning, sunset, etc).
3) I like the subject - interesting buds, great color. I would crop in from the left to remove the two buds not facing the camera as they are a downer compared to the two buds facing the camera. Also, the way the two main buds overlap has them competing for attention. I would either shift my position slightly or (if they are on different stalks) move one of them. Nothing says nature photos can't be staged.
4) In my opinion the weakest of the set. This perspective seems to be trying to emphasize the height of the tree - in that case portrait orientation is called for. If there were a more interesting pattern to the limbs, increase your DoF to include them - then keeping it in landscape orientation is fine. As it is, the tree just isn't that interesting, and the section of the bark that is in focus doesn't do anything for me.
5) Probably my second favorite of this set. I like the angle from which you shot the statue and the composition of your frame. Good use of DoF to blur an otherwise busy background. It's still a bit distracting, but sometimes you just have to deal with what you have to work with. I think this subject calls for, if anything, a bit of underexposure. The character of a sculpture like this is enhanced by the shadows created by its texture, so embellish rather than minimize the shadows. (Looking more closely, it looks like your focus may be a bit too close to the camera. Ideally, just like a human portrait, the sharpest focus would be on the eyes. In that case you would likely have had a bit less of the dish and a bit more of the hair in focus. You didn't miss by much - if you did in fact miss at all - but I see so much of the dish in focus that it almost draws my eye away from the face.)
I seem to recall another of our threads questioning your eye (or training your eye to see potential shots). From these I'd say you have a good start and are doing a good job experimenting with what's available.