Most often when I look at fantasy maps, first I notice if the geography is clearly nonsense* such as rivers flowing away from the oceans and towards mountains, peninsula not pointing at islands, lakes that somehow have several outlets instead of one, or major cities just plopped in some random spot without things that would justify a city like bays, rivers, a chokepoint if it's a military encampment, or arable land. Also, I tend to get irrationally angry at perfectly straight mountain ranges and oceans that turn 90-degree angles in order to box in the sides of the map.
Most fantasy maps fail at these simple standards.
From there I usually want to see if there's a follow-able path the heroes will take and interesting locations for them to visit to promote the story.
*If the world is clearly operating according to fantasy physics this need not apply, if there's a floating continent, crystals growing out of the ground the size of mountains, or we go really crazy like the world of Septerra Core, things are sufficiently wonky that I won't try to judge the rest of the map by contemporary geology.