[UPDATE: This article originally implied that Garry's Mod was a Valve franchise, which is erroneous. Corrections have been issued to clarify that, while published by Valve, it would not have anything to do with ever being revived, if so. We apologize for the mistake.]
Gabe Newell, founder and president of Valve, recently stated in an interview that Valve has multiple games in development with announcements to follow. While some fans are speculating that Gabe Newell could be referring to the long awaited Half Life 3, there are a number of franchises that Valve could revive given the recent success of Half Life: Alyx.
Gabe Newell implied that Half Life: Alyx has created a momentum in Valve to return to making single-player games. While Valve has reportedly been developing on a number of games over the years, they have subsequently been scrapped or cancelled. With Valve's commitment to creating new games, this hopefully signifies the rebirth of some forgotten franchises.
Half-Life Series
Known as probably the most famous Valve series, Half-Life 3 has had fans waiting for over a decade now. The original Half-Life was a first-person shooter that allowed players to assume the role of Gordon Freeman, a scientist who must escape a facility after it is overrun by aliens. It was followed up with a sequel, Half-Life 2 in 2004 and two extra episodic sequels titled Half-Life 2: Episode 1 and Half-Life 2: Episode 2. Over the years, multiple Half Life games have been planned but subsequently canceled including Half-Life 3 and Half-Life 2: Episode 3.
With the recent release of Half-Life: Alyx, it seems that Valve is ready to jump back into developing single-player games once again. For a while now, Valve has been coasting off the success of its digital distribution service, Steam, and its esports titles in Dota 2 and Counter Strike: Global Offensive. However, with Valve planning to announce some new games soon, it hopefully implies that the long-awaited Half Life sequel will finally make an appearance. Despite the fact that fans have been waiting for over a decade, there's still plenty of excitement for the return of Gordon Freeman. Moreover, the fact that Half Life: Alyx was so critically acclaimed despite being limited to VR should be an exciting prospect for the series' direction.
Portal Series
At this point in time, Portal 3 is probably the least likely sequel that Valve would make. While the Portal series is universally acclaimed, the story at the end of Portal 2 gave fans closure, and Valve has likely shifted its focus to other series. Many of the original staff that were part of the Portal series have left Valve, and much of its success relied on the quirky, yet dark narrative from the writers. The series itself is far from forgotten, though, and it wouldn't be surprising if Valve's new titles were related to the Portal series in some way.
In fact, Valve has revisited the Portal universe in 2016 when it released The Lab, a VR showcase game that takes place in Aperture Laboratories. Together with the Portal 2 level editor on the Steam Workshop, the series as a whole still appears to play a role in Valve's identity. Though Portal 3 is unlikely to happen, the Portal universe as a whole still has a lot to offer.
Team Fortress Series
Team Fortress 2 is often called the "forgotten child" of Valve as its development and updates have slowed to a halt with the success of Dota 2 and Counter Strike: Global Offensive. The first Team Fortress was originally a Quake mod that Valve ported to its Half-Life engine as a way to promote the Half-Life series. Eventually, Valve would release a sequel, Team Fortress 2, a class-based shooter with unique, cartoonish graphics and light-hearted gameplay.
Although Team Fortress 2 had some support in its competitive scene, it never grew into a full-fledged esport, and fans often cite this as the reason for Valve setting the series aside. With the announcement that new projects are in development at Valve, however, Team Fortress could see a revival, especially given how popular the genre has gotten. Character-based shooters like Valorant and Apex Legends have taken the world by storm, and a new Team Fortress game could prove to be just as popular.
Left 4 Dead Series
The Left 4 Dead series has a wonderful reputation, but despite its popularity, Valve has repeatedly denied that a third game is in development. Although there have been a number of rumors over the years as well as evidence for a cancelled Left 4 Dead project, Valve announced last year that it had stopped working on anything related to the franchise for a number of years. Still, the Left 4 Dead series is extremely popular and Valve hasn't closed off the series for good yet.
With the success of Half Life: Alyx, there are a number of possibilities for franchises to appear on VR in the future. In particular, the Left 4 Dead series could make fantastic use of VR given that there's a lack of co-op VR games currently available. Even if none of Valve's new projects end up as a new Left 4 Dead game, it's likely that it will influence the new games given how well-designed its co-op mechanics are.
Bonus: Garry's Mod
Originally conceived by Garry Newman of Facepunch Studios, Garry's Mod is a sandbox game that was created as a mod for Valve's Source game engine. Valve published it, but does not own it in anyway. It would have nothing to do with it being revived, but at the same time, it is a game deserving of it.
Although the base game had no objectives, players were able to spawn and manipulate assets from various Valve games. Over time, user-created game modes began to gain popularity and some were eventually turned into standalone games. Garry's Mod also influenced a lot of young talent that would go on to succeed in the indie development scene.
While Facepunch Studios has been working on its survival game Rust, there have been a number of rumors regarding a sequel to Garry's Mod over the years. Garry Newman announced a spiritual successor to Garry's Mod back in 2017 titled Sandbox that was reportedly being developed in Unreal Engine 4. However, Newman recently switched over to Valve's Source 2 engine, which has a lot of potential given that games like Dota 2 and Half Life: Alyx were created in the Source 2 engine.
Half-Life: Alyx is available now on PC.