Now I'm not exactly a fan of 9-Ball but love watching the game on TV since you can pick up many pointers by watching the players apply English, Draw, Follow, or Spin (or combinations of all). There has been a rise in 9-Ball popularity mostly caused by it being televised, and especially the women players of 9-Ball such as Karen Corr and Allison Fisher (ex-Snooker players from Ireland and the U.K.).
Their obvious excellent skills coupled with a rather short timeframe to play the game, make it an excellent format for TV as well as tournaments at Pool halls where the game goes by rather quickly. You'll find lots of people playing the game in bars as well since the rules are somewhat simple and arguments can be resolved rather quickly. There really isn't a notion of "the opponent's balls" since both players are after whichever ball is next in the sequence.
Not Fond Of 9-Ball
As I mentioned on my 8-Ball page, I don't like the "slop" aspect of the game. Doesn't seem right that the only shot I really need to call is for the 9-Ball itself (depends on whose rules you follow as to whether you even need to call the shot). Otherwise, you can make any ball in any pocket without calling it and continue to play. This means people can "get lucky" or "slop" a shot in and keep playing. Unlike 8-Ball, where if you don't call each shot to make, it's a ball in hand for the opponent. Limited, to practically no slop playing is tolerated. I also don't like it that I can do all the work, miss a single shot (on the 9-Ball), and then my opponent can come in and sink the ball and win the game. It's much easier to run the table playing 9-Ball when compared to 8-Ball since the opponents balls in 8-Ball are usually still on the table and hard to navigate around.
So that's my piece on 9-Ball. I still play it now and then but usually end up getting frustrated due to one shot I blow while remembering how my opponent did nothing to deserve winning, or a sloppy opponent that will luck a shot in. When this happens I think about how they would not get away with this in 8-Ball, however, that provides little comfort when I lose. I really don't even feel that good about winning since I know that it's an easier game to play and not truly indicative of how good a player really is. Note that many pro players actually play other games such as Snooker, Rotation, 8-Ball, or Straight Pool. It's just that those games don't get televised any more since they take much longer than a 9-Ball game. Of course Snooker is quite popular in the U.K. and you are apt to see it on TV just like we see 9-Ball on TV.
Show Me The Rules
Here's a PDF file containing the 9-Ball BCA Rulesheet. You may want to check with the BCA to be sure the rules are current but I try to keep on top of things so mine should be accurate. I've noticed they change the rules over the years to make the game more enjoyable for tournaments and television, but they don't really change all that much, more for clarification than anything else.