1) To play well it takes more skill than many other sports I've tried.
2) Your physical gifts can help you win (speed, strength, stamina)
3) Break points, game points, ad points and tie-breaks can happen quite often so the constant mental battle is a challenge.
4) I can and have been beaten by weaker, slower doubles players because they have more skill. My physical advantages on those occassions didn't matter. I like the fact that in tennis a weaker slower doubles pair can still easily beat a stronger fitter pairing.
5) On court the best feeling is ripping a clean winner or ace.
6) I like the gear especially the racquets
7) It's a non-contact sport.
It's outdoors and in sunny weather you can top up your tan.