I have developed a simple scale on which I rate DeFRaG maps for the game Xonotic.
Route - How complex the map is. A 10/10 can be completed without bhop or zhop with no issues while providing a challenge to the advanced players.
Readability - How easy it is to understand the map. In a 10/10 map the player clearly knows where they can go and where they are not allowed.
Style - Subjective, but for some reason it is much nicer to run maps with really good visuals than gray walls with the default textures.
Route: 10/10 - The map has a long route and many shortcuts and features a slick section. It is very simple to complete with a very high skill ceiling.
Readability: 8/10 - It is mostly obvious where to go, but some sections are unclear.
Style: 10/10 - The map has a lot of attention to detail, much more than any of the other maps I seen.
This list is short but will be updated over time.