Criteria for effective logo design
First, you can look at my work to get a sense of the type of execution I provide for design solutions, but here is how I measure the quality of those solutions for a logo design...
Simple: reduced to it's most necessary visual form, and still able to evoke or engage.
Appropriate: relevant to the industry, target audience, and needs defined.
Memorable: distinct enough to stand out from the crowd, not appear commonplace, and creates retention.
Conceptual: rooted in a good and strategic idea, be it literal or abstract.
Timeless: not given to trends or fashions, so as to be enduring as long as possible.
Graphic: recognizable even when words or type are not always legible, and functional in it's most basic form.
Gestalt: through visual suggestion, more is expressed than the total elements might indicate.
As you can tell, this list and my approach does not leave much room for superfluous effects like glows and drop shadows.
Now, a logo is the signature to the larger identity of an organization. It cannot answer every need, nor suggest everything. But, a logo does provide ownership and recognition as it is applied to materials, experiences, and communication that make up brand's image. Through exposure and time, viewers will begin to convey more meaning and purpose to the logo as they learn about the organization (whether it be positive or negative).
This is especially true with symbols. An example is Apple Inc., the design is anything but technical, but over time the image has rooted itself in people's minds as something that stands for high-quality, innovative technology products.
Similarly, a logo does not have to be a direct reflection of what your company does or sells. If Apple Inc. had used an image of a Macintosh computer when fleshing out it's logo years ago, then translating that symbol to apply to it's newer products and ventures (iTunes, iPad, etc.) would not have worked; as those things don't look like boxy computers. But the symbolism of the more "abstract" apple image design does work when applied to any new undertaking they pursue.
A logo and visual identity are part of your company's personality—your brand image. It's a flag that your loyalists stand behind; it's a badge that your employees wear; it's a face to your organization that potential customers see each day.
What makes a great identity?
A logo and supporting brand materials that are distinct, clever, memorable, simple, adaptable, on-target, and help create retention of who you are in people's minds. The designs should be personal and help people relate to you.
Think of iconic logos like the CBS eye, Coca-Cola script, and I 'Heart' NY. People have the opportunity to embrace these when first introduced to them and then reacquainted over repetitive and consistent use. Thus, they can make a connection to your company, and hopefully, it's the right one. Additionally, a logo needs to be applied in an engaging and strategic manner to all sorts of informative and promotional material to support it and build your visual image.
Identity design, a discipline of graphic design, is the bridge between business, art, and people.