There's no solid definition for what a logo is or should be. You won't find too many designers that agree 100% on what makes a good one or a bad one. Taste is subjective too, even really terrible logos have their fans. But, I can tell you what I think a good logo is.
I'm not going to tell you any magical secrets to logo design or that every logo should follow the same set of rules. Some logos need to do different things than others and they follow their own rules. Some make use of a clever idea and pull something personal from the thing it represents. Others are just for "performance" and need to do their duty, like sit in the corner of a webpage and identify what that page is. Some represent a culture with a specific concept, pattern or color (sports fans think of the Tampa Bay Buccaneers and Seattle Mariners), while others express a single idea well and are built to be absorbed by it's audience and become a permanent mark of the culture later (think Indianapolis Colts and Chicago Cubs).
Either way is fine, but understand that no logo is born with emotional value. That is earned over time, which we call equity. Most people don't like change and would rather their favorite brand hang on to the shitty logo they've always known than replace it. If it's a new logo/brand there will be many haters of it once it's debuted. It gets understood and accepted and loved over time.
What I will tell you about logo design is only what I can tell you. My views on logos are defined by learning from other designers, my own education, and my own experience. . . and a lot of time being a dork and thinking about logos. If I could sum up what a logo is, it is a thumbprint. To sum up what it does, it identifies something, then communicates a message about it.
Logos, like all design, send a message; and whether you're doing something personal and clever or just something to perform well, there is always a conversation with it's audience. Design is not all about aesthetics. Aesthetics are the least important thing about design. Your ideas and connotations and emotional responses to design are what makes it valuable and good. Form follows emotion. And study your history too. Colors and symbols can easily pull mental images of the wrong thing if you're too focused on aesthetics and visual performance. I like to use the example of the worst idea in Pro sports branding history: Putting a team named the New England Patriots in a red jersey and white pants.
That football uniform looks great, doesn't it? . . . But the concept fails.
What I use to define a good logo is a set of measures that I believe in fully, but I don't think all of them need to apply to every logo. Again, some logos just need to do different things. I start with the idea and emotional expressions. You don't need all 3 every time, but if you can capture the 1.) Personality 2.) Culture 3.) History, of something in a single logo, you've got a great concept. And those are listed in order of importance. Design always has a personality though, so make sure you're expressing the right one.
The next set of measures is about the performance of the logo and the more tangible aspects of it. These are the duties that need to be carried out by the design. If a logo "works" well, then it does these things well. Sometimes, a few of these are all you need. There's some overlap too, for instance simplicity helps visibility and memorability, good color choices help with distinctiveness, etc.
Visibility – Readability and clear form, even at small sizes.
The end result of a good logo should be something people are proud of. Something that you wouldn't mind wearing on a t-shirt. And, if it's a sports team especially, try not to design something that it's rivals can easily make fun of. My personal redesign of the Indianapolis Colt's horseshoe was said multiple times to look like a toilet seat. . . well, fuck!
Check out some of my favorite logo designers:
Fraser Davidson - Marc Verlander - Kris Bazen - David Airey - Tin Bacic - Jan Zabransky - Gert Van Duinen -