It's true that most players can be infuriatingly narrow-minded (especially in the CS community) when it comes to new maps, but that should be embraced as part of the challenge of mapping.
The most common mistake I see most mappers make is that they get snowblind by their own design. Once you've put the time in to design, build and tweak a map you develop a metabolic familiarity with it that no other player in the world will probably ever experience, so it can be disconcerting and infuriating to watch other players lolloping around it for the first time. The most controversial of Cottons streamed "reviews" was undoubtedly for de_sparity, partly because of 3click's outspoken reaction, but mainly because it's a map that was developed very publicly, so a lot of its fans had also developed some of that designer snowblindness and couldn't appreciate Cottons criticisms. Personally I think most of what he said was spot on for that map. Considering the number of maps he had to get through I think he was remarkably fair and diligent, and thankfully he wasn't the only judge.
When we playtest new layouts on the mapcore server, the first thing I look out for is whether one or either team adopts any sort of coherent strategy on the first round of each half. If they don't, the level designer has failed, in my opinion. It may be harsh to write a layout off so quickly, but that's what most players will do (simply because there are more maps out there than anybody has the time to enjoy) so that's the attitude you have to design for.