More Xbox 360 games have arrived on Xbox One today thanks to the latter’s backwards compatibility feature, but not all 360 games behave when played on Microsoft’s latest console.

Eurogamer’s Digital Foundry has published an in-depth look at the performance of all of the Xbox One’s Xbox 360 games available up to this point, and while it praises how well Microsoft has integrated backwards compatibility into the console, it has found a few games it claims are unplayable.

“Based on a wealth of extended testing, capture and analysis we can safely say that our experience has been positive,” writes Eurogamer’s John Linneman.

“Games generally operate without issue, but that doesn't mean there aren't a few hitches here and there.”

Eurogamer’s general findings: games appear somewhat darker on Xbox One and feature a slight improvement in upscaling quality, screen tearing has been eliminated, and hard drive and disc access operations tend to have less of an impact on performance.

Even so, emulating the Xbox 360’s PowerPC tri-core CPU appears tricky, so while Gears of War is deemed “playable, often with improved performance”, and Gears of War 3 is “playable with some performance issues”, Gears of War: Judgement is “nearly unplayable due to severe performance drops”.

Halo Reach is also deemed “nearly unplayable”.

You can read Eurogamer’s verdict on other backwards compatible games here.

Meanwhile, here are the 10 titles added to the service today:

The Witcher 2: Assassins of Kings
Sam & Max Save the World
Aegis Wing
Counter-Strike: GO
Age of Booty
Space Giraffe
Jeremy McGrath’s Offroad
Small Arms

The Witcher 2: Assassins of Kings is currently free for players in the US, Canada, United Kingdom, France and Germany, but not players in Australia and New Zealand.

Microsoft also announced that rather than release games to back-compat monthly, it will release titles as they become available.

To date, Xbox gamers around the world have logged more than 21 million hours playing Xbox One Backward Compatibility games, it added.