וַיַּ֤רְא אֱלֹהִים֙ אֶת־כָּל־אֲשֶׁ֣ר עָשָׂ֔ה וְהִנֵּה־ט֖וֹב מְאֹ֑ד וַֽיְהִי־עֶ֥רֶב וַֽיְהִי־בֹ֖קֶר י֥וֹם הַשִּׁשִּֽׁי׃ (פ)
Iddio vide, che tutto ciò ch’egli aveva fatto era molto bene. Così fu una sera, e fu una mattina; (cioè) il sesto giorno.
Rashi on Genesis
יום הששי THE SIXTH DAY — The letter ה, the numerical value of which is 5, is added to the word ששי when the work of Creation was complete, to imply that He made a stipulation with them that it endures only upon condition that Israel should accept the five books of the Torah (Shabbat 88a). Another interpretation of יום הששי THE SIXTH DAY — The whole Creation (the Universe) stood in a state of suspense (moral imperfection) until the sixth day — that is, the sixth day of Sivan which was destined to be the day when the Torah would be given to Israel (Avodah Zara 3a).
Rashbam on Genesis
וירא אלוקים את כל אשר עשה והנה טוב מאד, G’d reviewed all that He had done during these six “days,” to see if anything needed adjustments or improvement, but He found that everything was very good.
Sforno on Genesis
את כל אשר עשה והנה טוב מאד, the accomplishment of a project containing many different parts is greater than the accomplishment of each part of such project successfully. Now that G’d had completed the entire project successfully, the Torah described this with the additional word מאד instead of merely טוב.