There are multiple capturable objectives that can be held by both the offense and the defense teams. Some examples of the aptly-named points are 'radar station' or 'airfield' which provide obvious benefits (like radar and air vehicles, imagine that). There is also a point named "Golghari" where the forcefield generator for the defenders is housed. It is only by capturing this point and destroying the generator can the defender's base be infiltrated and the switch be captured.
In the pickup game, I didn't know about this generator and was assaulting their HQ island over and over but to no avail. Meanwhile, one of the players on the other team (who happened to be Morgoth Bauglir the map creator) held Golghari almost the whole map until I figured out what I was supposed to do. I didn't figure it out in time to actually capture before the time limit. Then, the positions were switched and his team won in 2 minutes or so. The moral of the story is, read the paragraph in siege maps that explain what to do.
Excellent map to play, it can be won very fast by a skilled team (They would be wise to capture an airfield). What I found most interesting is that you spend more time assaulting the Golghari point than the actual HQ base. This in of itself makes the map unique.