This collection is among the first released after the transition to the CS2 era. Valve followed the trend of adding awesome artistic images even for low-rarity skins. For an extremely low price, you can get amazingly beautiful cosmetic finishes. The Gallery Collection is a kind of exhibition of wonderfully creative ideas.
Just take a look at R8 Revolver | Tango! The roses and the wooden grip turn the pistol into a masterpiece—and the skin is totally accessible. If you are not keen on such a style, consider getting P90 | Randy Rush or SSG 08 | Rapid Transit. They represent other art directions: like a playing-card fantasy, and a representation of subway plans.
Sure, the most valuable items in the Gallery Collection fully unleash visual beauty. M4A1-S | Vaporwave, AK-47 | The Outsiders, and Glock-18 | Gold Toof may have little style connections, but all create an interesting atmosphere.