I don't know the specifics of the map round challenge in this year's RPG Superstar yet, but I'll discuss encounter maps because that's the type of maps that I'm most familiar with.
- The 75% rule: What I call the 75% rule means that any map element (wall, rubble, water, change in elevation, etc.) that somehow marks a border between two areas on the map shouldn't split a square 50/50. For example, if a thin, diagonal wall splits a square 50/50, how do you know on which side of the wall a creature standing in that square is? Or is it even possible to enter that square? If rubble covers 50% of a square, is it difficult terrain or not? To avoid this problem, my recommendation is that the "dominant" map element should always cover at least 75% of the square.
- Terrain to interact with: Some players love crazy stunts. A good map has some things with which the PCs can interact (destroy, move, climb on, jump down from, etc.) Allow the PCs to use their skills also in combat encounters.
- Make every part meaningful: As a player, it's very frustrating to walk through dozens of small rooms if there's nothing of interest there. Each part of the map should be useful somehow. If a room doesn't really make the map more interesting, consider leaving it out or combining it with one of the adjacent rooms or areas.
- Any map can (and should) feel sufficiently epic: Regardless of the party's average character level, any location they go to should be cool and interesting to explore and fight in. A great map does a lot to make an encounter memorable. A square, 15-by-15-feet room rarely feels epic. Bigger rooms with some variance in map elements (for example, difficult terrain, water, elevated parts, cover/concealment, and decorations of interesting, sometimes irregular/asymmetrical shapes) make the location much more memorable. Small rooms can also be fun if it's possible to move from room to room during the encounter. Small rooms that are just dead ends are not very interesting.
- Choose your route vs railroading: Much like the encounters themselves, encounter maps should also allow the players to make meaningful choices (or at the very least there should be an illusion of choice). Should I use Climb to attack the boss but risk falling down from a cliff or take the longer, safer and slower route and fight all the mooks first? Should I go "tanking" in the narrow corridor or go to an open area where I can use my mobility better?
As a player, what other map features do you like or dislike?