So I famously got my Holmes Basic set for Christmas 1980, and the rest is history. That delightfully primitive offering fueled months of gaming activity until I (inevitably) switched over to AD&D, with its slick hardcovers and expanded options. Mine shipped with B2, The (now-famous) Keep on the Borderlands, which was more than enough to get my nascent campaign going. It was an incomparable mix; but there was another MVP in that lineup which really started my juices flowing, and that was an awesome TSR catalog...
OK, so this thing did its job and made me want AD&D on day one. But there was so much more; and while I probably never owned half of it, the exposure nonetheless filled me with an excitement for what my new passion had to offer. There was Boot Hill, Gamma World, and Top Secret, which spoke to the endless of possibilities and secured TSR, at least in my young mind, as an established company. And even if I hadn't eventually gotten these, their mere presence communicated a single timeless truth: that anything was possible.
But it was the stuff I never bought that sealed the deal. From the spacey 4th Dimension to Divine Right, those little thumbnails suggested bottomless universes. There was aerial dogfighting Red Baron style in Fight in the Skies and the Arthurian romance of Knights of Camelot, the whimsical Snit's Revenge, and investigative chops of Suspicion. All of this communicated the possibilities of gaming; but the fact that I never owned these made them exotic and mysterious, adding immesurably to roleplaying's mystique...
So yeah, the catalog did what catalogs are supposed to do. It moved products. But the impressive volume of offerings, their breadth, depth, and hinted-at possibilities converged to suck me in and sell me on this lifelong passion. It also conveyed the (you'd think) obvious reality that I wasn't the only gamer out there, but instead part of a community. In short, these early catalogs (every boxed set it seemed came with another) sold me on the very idea of roleplaying, making it a true Gateway to Adventure for its fantasy loving devotees.