Most trashers fall into the category of 1) brute-force trashing (Chapel, Steward, Count, even Remake), which burn lots of cards but normally give you nothing in return, or 2) Remodeling, which turns a single card into something better.
Forge is the only trasher that can do both. It can trash lots of junk at once, like the brute-force trashers, but it can also turn some of your early buys (Silver, Steward, Moneylender, Sea Hag, Familiar, etc) into either stronger mid-game engine parts, or late game VP, while getting rid of junk in the process. And of course, it can also be Upgraded into a Province.