There used to be a thread that did this for me, but I can't find it anymore. There's a short list of things you should never, ever do in a map. You've violated the first one, and perhaps the second one (although the gauss turrets do have a nice shotgun-like effect), which is fine since you're pretty new. Just try to avoid them in the future.

1) Have large blocks of gold or multiple pieces of gold in one spot
2) Have multiple enemies in such a way that most of them are pointless
3) Place switches behind gold. Bounceblocks are questionable too, but there are a few cases where that actually benefits the level.
4) Place gold in unreachable areas, unless you're doing N art. Generally this applies to all objects.
5) Create a map that's impossible, or practically impossible, to beat.
6) Include large numbers of objects for no reason. Doors in particular can get very annoying.

Those are the biggest ones, and people will peg you as a newbie if you do one of these and generally won't look at your maps. #5, I've found, is particularly important - be sure to playtest your maps as well.