The Museum of Modern Art, which opens on Oct. 21, is not what it used to be — and not yet what it may become.

While still very much in progress, the museum could be on its way to its second round of greatness, to judge by the new presentation of the core collection and, even more, a series of inaugural satellite shows drawn from the permanent collection along with five new commissions. Together they underscore the vastness of the museum’s holdings, a sight that is staggering, possibly unprecedented and probably won’t recur until its next expansion.

It now has a new building with a new wing added almost seamlessly to its 2004 Taniguchi expansion. This is the largest home it’s ever had — a place , like the Metropolitan Museum of Art, where you can get lost. A psychological benefit is that the large (despised) Taniguchi atrium is de-emphasized. It doesn’t seem so big when you can get farther away from it.