If she's on form and playing well, yes. But the Serena that often shows up at regular tour events (except for the bit in the USO Series last year) these days is pretty bad to watch, but she gets the job done.
These days, she has glory days when she plays amazing (AO 07), but her movement is not as good as it used to be, so she might look sluggish and off-balance at times. Thank god she has that serve. As the poster above mentioned, she gets the job done these days
I'd say yes, although she is not the most enjoyable from a "pure" tennis perspective. HOWEVER, that was more true a decade ago than it is now. 10+ years ago (Serena's early career) you had Hingis, Davenport, Seles, Graf, etc. -- a lot of exceptional ball-strikers, volleyers, athlete's, and so on. Serena was a ball basher by comparison. Without such a field, and given that generation suck is so freaking one-dimensional, Serena's game SEEMS much more enjoyable even though it's actually regressed.
Obviously her serve is a sight to behold. Her movement used to be fantastic to watch, although I'd argue her footwork was always questionable. Today, not so much; she's quick but she definitely lumbers around the court, not pleasing to the eye. Her volleying is very average and her finesse is nearly non-existent, although once again when we compare her to Azarenka, Woz, Sharapova etc. she looks like Federer in those aspects of the game :tape: Her groundstrokes are a mixed bag -- technically sound, powerful, great angles, takes the ball early, but once again she is not as ferocious a shot-maker as she used to be, and errors can fly off her racket.
So overall, Serena is very enjoyable to watch, but she's no Hingis or Graf. But when the competition is Azarenka or Kvitova or Wozniacki, she is among the most enjoyable in today's game.