Jonas, as long as it is constructive criticism like yours I can take it any day of the week. You've expressed your opinion in a very clear manner and explained your points thoroughly.
Anyone who knows me around this forum knows I'm not a nature photographer at all (as a matter of fact this is probably the first picture of a bird I've ever taken), but it IS something I would really like doing more often and you have to start sometime. I've just received this 70-300mm and I was super happy about taking it to the zoo this weekend (I figured it would be better to start with animals that don't move much first hehehe) but I've got some bad flu and ended up staying at home all weekend...I was very frustrated and this little bird was the only thing I've managed to shoot so far (it was actually THE only shot I've taken of the bird).
Now, just to defend my self a little bit...this is a massive crop of the original photo, hence the over sharpened look. As for the framing, it's funny that you said you found the background distracting as it drew my attention for being so much like a camera's "framing grid" (I'm not sure if this is the word).
Anyway, you should not be "afraid" about sharing your thoughts as long as it is in a constructive manner. There are a lot of professionals around but there are also a lot of enthusiasts, amateurs and beginners. Everybody is here to share, learn and most importantly to have a good time.