XはYが(上手/下手/とくい)です as “X is(good/bad/good) at Y”
This construct is grammatically identical to the XはYが(好き/嫌い)です because it also derives from the TOPIC は SUBJECT が DESCRIPTOR form. Notice that both 上手 and とくい are both used to described goodness at an activity; the distinction is that while 上手 is used as someone else’s objective judgement, とくい is considered as a subjective analysis. When describing what you think to be your own talents, it is best to use とくい in order to convey that this is your subjective opinion that others might no agree with and not come off as extremely assertive of your skill.
Watashi wa video game ga tokui desu.
(I am good at video games.)
Anata wa nihongo ga jyouzu desu.
(You are good at Japanese.)
Watashi wa sports ga heta desu.
(I am poor at sports.)