Learn Spanish (Spain): Opino que el piso es muy caro. - My opinion is that the flat is very expensive.

In Spanish, the ending of the verb tells us who is doing the action. The -o on opino means "I opine" or "My opinion is". You can add yo for emphasis, making it yo opino, but it is completely normal and more common to leave it out.

I usually use creo que or pienso que. Is opino que different?

Opino comes from the verb opinar, which means to express an opinion. It means practically the same thing as creo (I believe) or pienso (I think) here, but it specifically signals that you are sharing your personal viewpoint rather than stating a hard fact.

Can I drop the word que like we often do in English?

No, you cannot. In English, we often skip the word "that" and just say "My opinion is the flat is very expensive." In Spanish, you must always keep que to connect the two halves of the sentence.

Why does this sentence use es instead of está for the price?

We use the verb ser (here as es) because being "expensive" (caro) is treated as a fundamental characteristic of this specific flat. Even though market prices can change over time, being a costly property is seen as a basic defining quality of the flat itself.

I thought meant the floor. Why does it mean "flat" here?