* SteamOS, Steam Machine, Steam Controller, Steam Link (2015) hardware, porting Steam, Source, and tooling to Linux (and patching Linux to improve gaming performance). Cross platform and streaming features. Facilitating porting of games to Linux.
* Source2 (2015) wrote a new game engine and ported DOTA2 to it. Neither is a small undertaking.
* HTC Vive VR (2016) hardware, software, tooling, and VR content. None a small undertaking.
* Valve Index (2019)
* Half-Life: Alyx (2020)
In addition, there were a few projects and games that never made it to market and a few I probably missed. I'm really happy to see them trying things nobody else is, even when they fail.
It's not like they released Dota 2 and that was that. They've kept developing it to this day at a breakneck pace, including even swaping out the engine like pfranz mentioned.
They aren't just a game development company anymore. Their primary product is Steam. If Half-Life Alyx was playable on any PC or console it would have been one of the best selling games of the year. Its only a niche product because, instead of resting on their laurels, they are trying to drive the industry forward.
Not only did they make the Index, which is by far the best VR Headset yet, they also supposedly helped HP develop the Reverb G2 that's coming out soon.
GabeN likes playing Dota but the idea that he sits around all day playing videogames when he's been building, improving, and expanding a billion dollar gaming empire is ridiculous.
There's also the massive progress towards making Linux a viable gaming platform. Really the only thing keeping me on Windows on my gaming system is the fact that most competitive multiplayer games' anti-cheat software can't run on Linux yet. If I played mostly single player games or casual multiplayer I could play almost everything I want to on Linux.
IMO they are plenty innovative. I wish they released more games, but aside from gaming they are doing a lot of great things for the gaming community.
They also did a good deal of the foundational work for VR working with HTC and Oculus. Then there's steam link, Steam controller/SteamOS/Steam Machines, Player created layers in Portal 2, Steak Workshop/Mod support (and paid mods) to name a few. There's a lot of not hits and a lot of not games, but they've been at least doing some stuff.
They are steam's landlords and hat makers, that's pretty much it.