Halo 3

Yeah that's my thinking too, I genuinely can't think of anything on either Xbox One or Series that qualifies, which is crazy when you think about it, to go two generations without a killer app. Really puts into perspective why they've been struggling these past 13 years.

Minecraft years before they purchased it.

I think it has been since Kinect Adventures in 2010. I don't know if Xbox 360 would've crossed 70 million units without the success of Kinect.
Halo: Combat Evolved was a killer app for a first console, despite Xbox falling well behind PS2.
Halo 3 was a killer app, so is Kinect Adventures. I don't know if there have ever been any other Microsoft titles that have been killer apps for Xbox. Shoot, there probably hasn't even been killer app third-party games even since 360 in general.

Gears of War was a killer app for the 360 I'd say; it was one of the most impactful blockbusters of the early 7th gen.

But yeah, it's slim pickings, which is really on MS for not cultivating the kind of system sellers Nintendo and Sony came to produce regularly.

Kinect Adventures was not a killer app, it was the Kinect itself that drove people to buy Xboxes back in 2010. The fact that Kinect Adventures was the pack-in game was incidental; it could have been Kinectimals as the chosen pack-in game and that would have technically sold 20+ million. Kinect Adventures on its own wouldn't have sold much.

It's odd how quick the mood shifted with Kinect. The logic was that Kinect 1.0 was a huge system seller for 360, so it was a no-brainer of packing Kinect 2.0 with Xbox One. Surely Kinect 2.0 was also going to be a system seller, but the audience had soured on Kinect in just 3 years.

The Forz Horizon games have been stellar for some time. I would consider those games killer apps. Besides Forza, Titanfall was a killer app for me. I got it as a bundle with my XBO.

Minecraft was massive already before then.... and everywere too.
Yeah it probably pushed hardware back when the xbox one s was like 199$.... as a gift for the kids to have a machine.
That was likely only ever used for like minecraft and roblox.

While Xbox's mistakes over the last 13 years have been innumerable, I think to me the lack of killer games is the single most crippling one.

Other stuff like the Xbox One's initial faceplant could have been overlooked or recovered from if they managed to provide killer games that made the system worth buying, but without that, all you were left with was essentially a worse Playstation.

The rest flowed from there; no killer apps meant hardware sales slumped, which meant their games couldn't sell enough, which led to them putting their games first on PC then PS/Nintendo, bringing us to where they are now.

The only reason I think you’re wrong with this is that you haven’t connected the dots. Kinect Adventures is a forgotten game, and as you mention it only hit those numbers because its was a pack-in.

Its what its was packed in with - Kinect - that was the system seller.