Most TV shows start to go downhill by the fourth season either through too many character replacements or repetitiveness of the episodes. Not Bones, out of the entire series I can count the number of episodes I don't like on one hand.
This is a great alternative to many of the main stream talked about crime TV series out there. This packs in realism, comedy, action, adventure, mystery, and psuedo-science all into one show with a cast that couldn't be more beautiful or enjoyable to watch week after week.
If you haven't seen any of these just buy season 1,2, & 3 you certainly won't be disappointed and it'll give you something to do while you wait for the DVD release of season 4. Also of note is that if you haven't seen season 1,2 or 3 you may be a little lost watching season 4 alone. The writers have done an excellent job maintaing continuity of the story line accross all the seasons so there will be many jokes, comments, and sub-plots that you simply won't understand without the past seasons.