My second oldest ongoing project (and the oldest I've shared with the public in any real capacity) has been a Team Fortress 2 clone which started as a idea for a TF2 balance mod. That game basically amounts to "TF2, but with new characters and fixing the things I feel are wrong with TF2 (namely, a loss of vision when it comes to weapon design and a loss of support for community server based play in favor of automated matchmaking)", and that game is a little too big in scope to work as RJS's first game, so this isn't about that game; this is about the game that leads up to that game - a small, singleplayer bit that introduces some of the main characters for an ongoing series that will, eventually, include a TF2 clone.
Rocky Bell's Rocket Romp is a "First-Person Platformer" based on the concept of "Jump Maps" made by the TF2 community. Rochelle "Rocky" Bell traverses smallish, mostly linear levels, using her rocket launcher to either destroy obstacles or maneuver around them by shooting the ground under her feet and riding the shockwave of the blast. Unlike classic jump maps that are mostly concerned with practicing advanced Rocket Jumping techniques, Rocket Romp levels provide less technically demanding but more dynamic platforming challenges, with moving platforms, enemies you will have to fight along the way, and other more unusual hazards.
Visually, Rocket Romp is based heavily on the look of the Mario Bros. series, and contrasts heavily with the expected aesthetic of a first-person shooter, a move evocative of how games like Twinbee and Fantasy Zone departed from the expected aesthetics of shoot-em-ups in the mid-80s. Rocky is a chipper and boisterous young woman whose design carries all the hallmarks of a 90s platformer protagonist, like a color scheme dominated by saturated primary colors and white gloves. She's also absurdly busty, but otherwise totally chaste in design, a decision intended to defy the trend of women, particularly large-breasted ones, being oversexualized in media. Her adversary is a universe-hopping alien named Ksyon who resembles an upright green tarantula (in fact, being the "Rocket Jumping Spider" after which RJS is named) and has come to Rocky's world to unearth and commandeer a sealed army of sap-based golems called "Ambers".
Out of all of the "first game" candidates, Rocket Romp is the one with the most relevance to RJS's long-term goals, introducing RJS's two central mascots, Rocky Bell and Ksyon, and setting the stage for the series that will form the backbone of the RJS library. If it's not the first game RJS releases, it will definitely be the second.