Hmmm... what makes a good designer?
The aspect here as at most places is quite a varied bag of beans.
Think of them as the manager of a Football team, you gotta have good imagination and creativity, you've gotta know roughly how it can be implimented, you've gotta have good communication skills.
It is all oki to have a wing'n'a'prayer idea ... but you have to have a very deep imagination which you can take the simplest of ideas, unreveal it like an orange and break it up into the segmants that are usuable by the other members.
It is actually more important however to understand howto explain something TO the Artists and Coders than it is to know roughly how it is possible.
As part of my job it is paramount to understand alot of aspects of 3D Programming as well as the artwork ... because if there is a new tool required, then we gotta work fast so little time is wasted.
People who are solo workers, or never speak up about anything - you'll have to work on that to become more team like, the best games have come from a great working team who understand each other.
What does happen in each company is oftenly different, because the work ethic here is more "don't over work just get it done right" ... whereas at Core it was more "we work until we drop"
which i've found is actually a very big difference between the UK and US companies, because alot of the companies here do have a more laid back attitude to games development. Whereas UK companies will oftenly work as hard as they can to get the games out ASAP.
There are ofcourse exceptions to these rules... ID Software and Rare Ltd are good examples.
The thing about working within the industry that a book can't explain is the dedication required to your FIELD of work. Yes you'll be expected to know about the others, but you'll never be expect as an artist say to pickup a keyboard and code... Knowing the techniques is what you require not actual skill in the subject.
Yes that is probably what oftenly seperates the Coders from the 3D Artists and 2D Artists and Designers and Character Developers etc...
There is a suprisingly ENOURMOUS different between a level engineer and a game modeler - I mean most people can do both, but a level engineer requires to think of bigger pictures and be able to run throu a world in thier heads, whereas game modelers need to be able to focus on the smallest of details.
These trains of thought are not easily compatible
I hope that is all helpful
Anata aru kowagaru no watashi! 
