Mascis is largely responsible for the resurrection of the guitar in indie music. With it, he made indie rock. Mascis coated everything in feedback (probably sowing the seeds for the shoegazer movement), played louder than anyone and cranked out incredibly expressive guitar solos, completely ignoring the underground's unspoken eschewal of them.
Merge has remastered and re-released Dinosaur Jr.'s first three records with some bonus features. The sound is only a little better, but at least the music is readily available again. The eponymous debut simply lacks a cohesive sound. It's too all-over-the-place to be worth purchase, but the songs "Repulsion" and "Forget the Swan" foreshadow the greatness to come on the band's next two albums, which are indie-rock masterpieces. Dinosaur Jr.'s second album, You're Living All Over Me, is where they hit pay dirt. Songs like "Little Fury Things" and "The Lung" are explosive from top to bottom and warrant repeated listens almost twenty years later.
Bug, the final album to feature the original trio (subsequent albums were really just solo outings for Mascis), includes the simple but powerful "Freak Scene" and is probably Dinosaur Jr.'s best batch of songs.
It's not hyperbole to say that independent music would sound completely different without Dinosaur Jr.'s influence, so if you haven't bothered before, it's high time you check them out now. And if you already have these albums, pick 'em up again -- for old times' sake.