i play tennis better than he does对不对？

对的。

形容词good和副词well的比较级都是better。

我打网球好。

I play tennis well

well修饰动词 play，我打网球比他打的好，二者比较用比较级，前后时态一致，所以此句可以为

I play tennis better than he/ him也可以为:

I play tennis better than he does.