I've just gotten my map, cp_backcountry, tested for the first time. Can someone who played it tell me what's wrong with gameplay (ik about bugs)
Read the feedback page for basic feedback. If you want in-depth feedback about the map, encourage others to write their feedback on the map's thread.
You can also what the demo of the feedback page, as some people leave feedback through voice chat. And you can watch how the map played.
If neither of those help you, I'm not sure what else to tell you. They're about the most help you're gonna get unless someone decides to write you an in-depth review.
It's not hard, learn to analyse the gameplay. Does an area give too much power to defenders/attackers. Become analytical, tear your map apart and see what makes it tick.
Did you test it on a gameday or an imp? I suggest you fix and do some of the things on the feedback list and then put it for testing again.