If we go by seasons, Star Trek Online has been the longest-running Star Trek-branded property of all, with the game's Season 10: The Iconian War update having gone live just this week. Of course, that's a bit of a cheat, as developer Cryptic Studios has opted to call all of the game's major updates a "season". In reality, the game's 2010 release has only given it sufficient years to outlast the original series and Star Trek: Enterprise. So far.
That said, the game might be one of the largest Trek-things around in terms of scale. The Iconian War pits the forces of the Alpha, Beta, and Delta quadrants against the Iconians, who are making its return to Trek fiction as a galactic threat that makes Mass Effect's Reapers look like a gang of street thugs. New story missions featuring voice work from Robert Duncan Mcneill, reprising his Star Trek: Voyager role as Tom Paris and Lisa LoCicero, who played Tom's daughter Miral Paris in that series' final episode.
New endgame raid events have also been added, in addition to new equipment, costumes, and starships to earn and buy. A revamp of the game's "Sector Space" world map makes space travel more interesting by removing the loading breaks from the original game's numerous "sector block" areas and consolidating it into three massive quadrant maps. The "Delta Recruitment" event is also still running, conferring benefits on new players and existing players that start new characters, so now might be a nice time to give the game a try.