The goal in Fantasy Defense is to protect your gate from the enemy gate(s). A road leads to your gate, and may have intersections or multiple paths. So far I have seen no more than two enemy gates, though the preview images of locked stages are hard to interpret. You buy units with gold and heroes with mana, both of which are gained from slain enemies. There are also items on the board that will give you gold or mana. Thus far none provide both.
|These are the bosses, btw.|
It is a fun game, and highly addictive. I play it far too much, and a big part of why the posting has been so thin of late (that and that I hate my computer but cannot blog on the iPad). So, look for it on your device of choice. Give it a whirl.