Forge World maps need more playtesting and should adhere to more stringent standards before being placed in matchmaking. Of the current crop of Forge World maps in Team Slayer, I can think of three that are absolutely horrid off of the top of my head: Think Twice, Precipice, and Select. Of these three, Precipice is the worst. The layout makes absolutely no sense and is entirely dependent on radar usage. The team spawns and weapon spawns are horrid, and map movement is confusing and slow-paced due to the design of the map. It's terrible.
TL;DR: Playtest maps more/create higher standards for community maps.
Note: Some maps, such as Rebirth and Synapse, are very well done and rival Bungie maps (Rebirth is fantastic and Synapse looks and plays wonderfully).