"Bad" can mean many things, including something that has "gone bad" (pourri, from the verb "pourrir", to rot). So can "rotten". The food is rotten. I feel rotten. That was a rotten thing to say. So it's best to think specifically about what you want to say. After you have mastered everything DL throws at you, you can branch out and learn a dozen other ways to say it.
i wrote "il semble mauvais" and was marked right, but the translation given was "they seem to be bad". was my answer meant to have been wrong?