This roommate seems better because the previous one was so terrible.
「前のルームメイトがひどすぎて、今回の人は普通だけど天使のように思える。」は英語で「My previous roommate was so terrible/awful, that my new roommate is normal, but seems like an angel in comparison.」という表現が良いと思います。
前のルームメイトーMy previous roommate
ひどすぎてーSo awful・So terrible
今回の人ーThis person・The new person/roommate
普通ーNormal・Ordinary
天使のようにーLike an angel
思えるーTo seem