What makes a "good Logo"?

I would like to know what you guys think makes a Logo a "good logo" what are some of the more rookie mistakes, and what makes a logo proffessional?

Lets take McDonalds over CocaCola for instance. Both logos are well known because of their products.
Although both popular I think the McDonalds "M" Logo sucks balls. Although its easily recognized there isnt much you can do with it but change the color. Even then its always fucking yellow. On the other hand its timeless they wouldnt have trouble sporting this logo in 20 million 12. It is just too damn bold and boring to me.

Now the CocaCola logo has undergone a couple of changes throught the years but not nearly as many as pepsi. I think its reached its timeless point. It is very highly recognized and has the potential for many creative styles. This Logo is so versatile that you can almost write anything with its text and it will be recognized by almost anyone.

I also think simplicity goes a long way.

So I was wondering whats makes a Logo a good logo?

i say something that grabs attention, can be easily remembered and is very unique. Logo's that look childish ruin places.

Generalise logo's like dolphins for a sea world center are rubbish because they all look the same, they need to be unique.