I was thinking about making an asymmetrical map because i need a break from casual maps and my symmetrical ones suck. So i'm asking, What makes an asymmetrical map good and what makes it have good gameplay and what makes them bad and have bad gameplay?
If it's asymetrical you're going for, try to thing of an original theme. Like a fort seige, only not, because that wouldn't be original. Anyway, they're the maps that are usually interesting, just don't forget to make them balanced. Good luck!
I like trying to make both sides different, but still balanced so one side doesnt have an advantage. An example of a bad assymetrical map would be, in my opinion, Guardian. At least the matchmaking version. One team starts with OV, Camo, and snipe, and its very easy to hold that side down too. A good assymetrical map would be last resort. The beach and the base are well-balanced and BOTH teams have a shot at getting all the power weapons.
You should be taking a look at what's being produced in the MLG Forge forums. Some of the designs and subsequent maps that are being produced (Hangout, Reverence) are very well made. The best part about these maps is that they're making these smooth-running maps without the budget glitch.
I feel the key to an excellent Asymmetric map, is Balance. Any map can look good, but the cherry and cream are the weapon and spawn balancing. Always have each player spawn in an area where they are going to have an equal opportunity of a better weapon than the default start one. As for layout, keep it interesting with a few chokepoints and open areas. Make sure there's a good flow and you don't have to double back on yourself etc.