Streaming video games is an idea with such obvious advantages that like virtual reality, motion controls and 3D screens, it had already hit the market several times before it was technologically possible: witness the untimely demise of OnLive in 2015. The big question facing Microsoft and Google, both of which showed off their entries into the “cloud gaming” market at the E3 video game conference in Los Angeles last month, is whether they’ve taken the plunge at the right time, or whether they, too, will be chalked up in history as premature entrants.

After playing with Microsoft’s Project xCloud and Google’s Stadia, we can draw some conclusions but others will have to wait. Both services are aiming at different targets, and based on the idealised situations in which they were presented, they each achieve their goals. But not everything is in their hands. No plan survives contact with the enemy, and no streaming service has yet survived contact with the realities of home broadband.

There’s a lot to like about the concept of game streaming. The cost savings of placing the expensive, complex hardware that is needed to play modern games in a data centre and streaming only the raw video footage to the player’s screen are significant. Data centres can efficiently power and cool their consoles, can keep machines in use 24/7 – or near enough – rather than having them sit idle for most of the day, and nobody has to go through the hassle of making and selling millions of machines to sit under televisions.

By moving the console to the cloud, games can be played on basically anything with a screen: a TV with a streaming stick, a mobile phone, a low-powered laptop. And where only the most dedicated players upgrade their console or PC more than once every four or five years, cloud gaming services can offer the most powerful devices possible, all the time, with no need for upgrades.

In practice, the reality often hasn’t matched the promise. Streaming services that already exist – from Sony’s PlayStation Now service in 2014 to 2015’s Shadow – have never had more than mixed success. Various explanations involving cost and marketing budgets have been offered, but underlying them all is the reality that getting a streaming service to work is difficult.

While YouTube and Netflix make it look easy, even streaming high-quality video is tricky. But for games, there’s an additional problem: latency. It takes a fraction of a second for an image to arrive on your home screen from a data centre and a fraction more for a button-press to get back to the data centre from your home. Those fractions do not have to be very high for a moderately fast-paced game to become unplayable and not much higher than that for almost any game to become unpleasantly sluggish.

Some of that delay is down to technology: the speed of your internet connection, the quality of your router, even the make of your TV all have an effect. But some of it is raw physics. A gamer in Houston, Texas playing on a data centre in Seattle, Washington, for instance, is a little over 3,000km away. Even if the data travelled at the speed of light there and back with no other delays, there would be a delay of more than 1/60th of a second – and one frame can be the difference between a win and a loss in a fighting game.

Both Google and Microsoft think they have what it takes to overcome those problems. In one aspect at least, they’re better placed than anyone to try: each company already owns an enormous cloud business, with data centres spread throughout the world, specifically placed to minimise the physical distance between their data and the greatest possible number of people.

With Stadia in particular, the result is impressively boring: playing Doom Eternal on the cloud gaming service feels exactly like playing it on a console. In the YouTube Space in downtown LA – a lavishly decked-out room for the company to host, entertain and feed free tacos to YouTubers visiting E3 – a row of TVs featured the latest demo of the forthcoming shooter game from Bethesda.

The setup wasn’t quite pushing Stadia to its limits. The screens were 1080p, not 4K, and the sound was stereo through headphones, not the promised 5.1 surround sound that will arrive with the full subscription version in November. But the game may as well have been running locally on a PlayStation 4 – when, in fact, it was running in Google’s cloud, wired in to a Chromecast. It was lag-free, artefact-free and remarkably unremarkable.

For its part, Microsoft’s demo clearly had a different goal. Resident Evil 7 and Halo 5 were playable, but rather than leaning back on a sofa and playing on TV, the screen was a mobile phone, harnessed to an Xbox One controller.

The games weren’t lag-free; there was a perceptible delay between hitting a button and getting a result, though it wasn’t enough to render either game unplayable, even in moments of fast-paced action. What’s more, Microsoft wasn’t playing on easy mode. The phone was connected to the internet wirelessly, rather than through a cable, which reflects how these devices will be used in real homes. Given that Microsoft’s demos were taking place in a crowded theatre with several hundred other devices all crowding the wireless spectrum, the result was impressive.

But both companies have questions yet to be answered that will affect their chances of success. For Google, these relate to whether their real-world performance can match that flawless demonstration in the YouTube Space. The company is pricing Stadia like a console, with an upfront fee for the controller, a flat price per game and an optional monthly subscription for added features (such as 4K) and access to a rotating catalogue of free games.

That may be OK, particularly if each game costs less than it does on a disc, but it makes it that much more important that the service is flawless. Phil Harrison, the head of Stadia, assured us that the company was able to provide the basic features for anyone with a 10Mbps connection, and the full 4K/5.1 surround sound version for a 35Mbps connection. But people have a right to be sceptical until they see it working in their own homes. It wouldn’t be the first time a company had overpromised and underdelivered.

Microsoft, meanwhile, is avoiding that problem by not really promising anything. The company has been unwilling to provide many details on what Project xCloud actually is. We know it will launch with a feature allowing Xbox owners to play games on their own console remotely – apparently akin to Sony’s Remote Play – before expanding to full-blown cloud-hosted gaming later. But important questions on pricing, availability and even release branding, remain stubbornly unanswered.