There are many digital libraries.  A set of DLs selected by participants in a seminar in SILS at UNC-CH were characterized according to a review template that follows.
 

Digital Library Review Template

DL Name
DL Address (URL)
DL Mission

Community
What is the user community(ies)?
Who are the stakeholders (sponsors, partners)? Who actually operates the DL?
How is the DL funded?  Is this sustainable?
How does the DL interoperate/cooperate with other DLs?

Content  (Collection Development Policy)
 What does the DL contain (type, media, volume)?
What will it contain in 5 years?
How is it organized (what are atomic collection units? Collections/aggregations? What metadata is used for each?)
 If the DL is part of a physical library, how are digital and physical objects related? (e.g., are there digital pointers to physical objects?

Services
 What is the access policy (e.g., open URL, partially open, membership, etc.)?
 What search services are provided (e.g., single search engine for entire DL? Alternative modes [e.g., basic, advanced])?
How is selection/browsing managed?
Are reference services offered (e.g., FAQ, email queries, query form, etc.)?
 Is help or instruction available?

Technology
Where do the files/dbs/server(s) reside?
What are the hardware (compute and network) components?
 What interface techniques are used (assumptions about user expertise, interaction style supported [command/form-fill/menu/direct manipulation/visualizations], control mechanisms provided [frames, java apps])?
Are there special security or quality of service provisions?
Are there specific research and development problems this DL addresses?

Publications, related URLs, etc.

Course Syllabus: www.ils.unc.edu/~march/courses/310_s99/syllabus.html