What makes an annotated game useful?

Perhaps it's better to ask what makes an annotated game most useful.  There are quite a number of things that we can look for in annotations, for example:

• Openings guidance - traps to avoid, identification of critical lines, explanations of typical ideas and choices
• Comparison of possible middlegame strategic plans, including ones not chosen
• Examples of combinations
• Key tactical ideas, either in the game itself or in variations
• Methods of conducting an attack
• Methods of conducting an effective defense
• Understanding of key turning points in the game and how they came about
• Evaluations of positional factors
• Endgame strategies explained
• Endgame technique explained
• Meta-factors - these include things like the tournament standing of the players (does one need a win desperately?), personal rivalries, and past history of their meetings

Any game containing all of the above is sure to be very useful for the improving player's understanding of the game.  But how often do you see that?  Rarely, of course.  But some works do offer us this kind of high level of utility

• Logical Chess Move by Move by Irving Chernev was the first book I completed after starting this blog.  Not all of the games contain all of the elements described above, but on the whole the collection does cover all the bases, at a level of explanation geared toward the club player.
• I also own John Nunn's Understanding Chess Move by Move and read it a number of years ago.  I will definitely return to it, hopefully with greater concentration and deeper understanding.
• I'm still working through Bronstein's Zurich International Chess Tournament 1953 on my lunch hours, when possible.  His game annotations vary in depth but are among the most useful and engaging that I've run across.  Naturally those of his own games are very insightful and his willingness to present a critical view of his own thought processes and actions is quite refreshing, as well as instructive.
• Anatoly Karpov's How to Play the English Opening is an outstanding example of instructive, high-level GM annotations.  Rather than produce a standard opening manual, Karpov annotated a large number of illustrative games in the English at the professional level.  As I noted in the original post, it's not for the faint of heart, although a focused club player should be able to keep up with most of it.

Perhaps you have your own favorites.

I also find it fun and valuable to look at annotated games from ongoing international events, for example those posted on the Chessbase news site.  A recent report on the Polish Team Championship drew my attention for the helpfulness of the two game annotations it contained, particularly the fact that explanations of ideas at key points were provided.  This sort of thing also shows that it doesn't take a huge effort to produce annotations with valuable insights.

While we're on the subject, I think it's also worth re-emphasizing the utility of annotating one's own games as a method of improvement.  In fact, it's hard to see how someone can make significant progress without analyzing and better understanding their own play.  As a somewhat crude example of this, it's been a bit embarrassing for me to repeatedly publish games with the same basic errors in them, for example in the Caro-Kann Advance variation series.  In the past I neglected this type of analysis and as a result simply wasn't even aware of the need to correct my play.  The implications of this for my performance at the chessboard are obvious, as are the benefits of doing game analysis now.

As a final note, one doesn't have to be a master-level player  to usefully annotate games, especially if they're your own.  Some other bloggers in the chess improvement community have done similar things and I'm always interested in seeing what they come up with.  My previous favorite example was TommyG's blog (now defunct) as it was always entertaining to read and the game annotations, which were geared towards self-improvement, I found both useful and motivational.