Many of my friends think the idea of a whole book devoted to a shell is bizarre, but that is more of an objection to bash (which is a bit on the baroque side) than anything else, and I won't enter into the relative merits of different shells. If you are (say) a novice Linux user, then Learning the bash Shell contains more than you are likely to want or need at first: the brief summary in a more general book such as Running Linux will be enough to get you by. If you start to do any sort of serious shell programming, however, Learning the bash Shell would be a most useful volume. Whether those who are familiar with other shells find it worthwhile will largely depend on how comfortable they are with the bash manual entry.
Note: Learning the bash Shell was updated with a third edition in 2005.