If you have the patience for them, the original Metal Gear and Metal Gear 2: Solid Snake are included in every edition of Metal Gear Solid 3 from the “Subsistence” PS2 rerelease onward. So they’re included in the HD Collection and Legacy Collection, but you have to go start MGS3 and go into its extras menu to find them.

Note that you’ll almost certainly need a guide/walkthrough for them, especially for MG2:SS.

They’re not essential (and MGS1 is largely a remake of MG2:SS in 3D, though it is also a sequel and references the events of MG2:SS throughout), but I enjoyed them.