After a PUG here last night (after begging my clan to do one forever and ever until we finally had to do one because it's in UGC...), I can safely say that this is the most unique new 5 pt map without a doubt. The flow of the gameplay is incredibly different and provocative, I'm not sure how the larger community will respond.
The angles and lines are all very well crafted and there wasn't much that seemed unbalanced, although the major concerns did seem to be that it tended to become a spamfest (with 6v6) between points. Middle, though, we all agree is amazing! The design of last is great and it requires a lot of coordination to defend, so maybe the problem is localized around 2nd? If I had to venture a guess, I'd say that your tunnels are just funneling all the energy teams have when they successfully take mid or 2nd and putting a point on it, making it either very easy to defend with spam. The fix may just be as simple as widening the doors or tunnels, but who knows.
<3333 & Awesome Work!