Sturgeon's Law says "Ninety percent of everything is crud", and it applies to blogs too. The vast majority are self-indulgent drivel, but a few are informative and interesting, e.g. Pharyngula (biology & evolution) or Juicy Studio (web design), and there are great posts on other blogs, e.g. Deadly Genius (how the arts lost touch with the public in the early 20th century).
OK, a lot of even the good blogs are derivative, but if you learn which blogs you like they point you to material you find interesting - pretty much like the old media, including the WSJ.