That movie was interesting only up to half-way. Then from half-way it became boring so I stopped watching it.
ご質問ありがとうございます。
「あの映画、途中までは面白かった」は英語で「That movie was interesting only up to half-way.」と言えます。
また、追加に「(途中から)つまらなくなったので、(途中で)みるのを止めた」と言いたいなら、そうすると、「Then from half-way it became boring so I stopped watching.」になります。
全体的に「That movie was interesting only up to half-way. Then from half-way it became boring so I stopped watching it.」になります。
ご参考になれば幸いです。
That movie was interesting up to a certain point, but it became boring after that and so I stopped watching it.
ご質問ありがとうございます。
この文脈では「途中」を"up to a certain point"(ある特定の時点まで)と訳しました。
"That movie was interesting up to a certain point,"=「その映画はある時点まで面白かった」
"but it became boring after that and so I stopped watching it."=「でもその後はつまらなくなったので、見るのを止めた。」
ご参考に。