I've never been a big fan of the Spectre or Captain Marvel (Shazam!). But magic (and the spiritual world) play a big part of the DC universe, and apparently what happens in Infinite Crisis affects magic (though I don't know the IC story yet...that's coming up soon for me). It actually is a pretty good story, though it contains few DC folks I care about (though Superman is found in the beginning). Very important to understand the DC world after IC.