A dozen different people might define the characteristics of a good manager in a dozen different ways, but maybe the differences are only in the details, while the heart of the matter is essentially agreed on. Perhaps, above all other factors, a good manager needs enthusiasm and passion for the job. Without that, the job is lost before it's begun, since it's impossible to maintain long-term interest and dedication from employees if they believe the manager is just putting in time.
A firm but understanding hand is required by a good manager, especially considering the variety of personalities and temperaments he's likely to encounter from employees. He should take care to hire carefully and not be afraid to fire when warranted. Also, to successfully manage a team or department means you should actually enjoy being around and interacting with people. Microsoft founder Bill Gates made a good point on this topic when he suggested that being a people person is hard to fake.
Too many managers find it difficult to make hard or sometimes even easy decisions, and put them off until there's no more need to even make it. This is not managing. The ability and proclivity to embrace the decision-making process is crucial to management. Don't let tough problems languish while you dither about what to do. Gather information. Ponder the options, consulting with your own supervisors if necessary, then make the decision and let the chips fall as they may.
Different jobs require different work environments and the manager is the one to realize the best way to arrange the worksite to get the most from his people. If the work requires brainstorming and input from co-workers, it doesn't make sense to have everyone confined to separate offices; it might be a good idea to create a common area. If tasks involve research, thinking, and writing, individual offices are preferable.
It helps for a manager to have a technical understanding of how the business of the company is accomplished. For example, if Megacorp A produces widgets, the manager needs to understand exactly how it is his team puts their collective brains together to produce the best darn widget on the market. Another example from Microsoft is that Gates was himself a software engineer. Even as he found his time monopolized more and more by running his business, his employees knew they could still come to him with particular problems that arose with software development and he'd understand what they were talking about.