A few things that I've been thinking about...
Personally, I like songs that is a more of a production/creative challenge, like 9, 10, 12, 15 & 18 for example. Nothing wrong with a plain rock song, but the two are very different exercises imho.
I agree that a high trackcount is preferable.
To get the critique/feedback thread going we could just agree to comment on the previous 5-10 mixes in the submission thread. That way it becomes a less daunting task when we're dealing with 20-30 mixes.
All the best,
Stefan
SingSing