ほど～ない

ほど～ない means "not as … as". The thing you are describing takes は, the thing it falls short of takes ほど, and the sentence ends in the negative.

The noun before ほど is the one with more of the quality. A verb works the same way as an adjective: かれ彼ほどれんしゅう練習していない, "I haven't practised as much as him".

ほど or より

より says the same thing from the other side, in a positive sentence. ほど needs the negative.

• × 大阪は東京ほど小さい → 大阪は東京より小さい

思ったほど～ない

A た-form before ほど sets the standard as what you thought or expected beforehand.

それほど～ない

With no noun to compare against, それほど or the more casual そんなに means "not that …".