Microsoft added Halo: Reach to the roster of backwards compatible games for the Xbox One earlier this month, but it looks like the game is suffering from framerate issues on the console. Several users have taken to Reddit to state that the game is "unplayable," with framerates going down to less than 10fps during battle sequences.
Microsoft has informed Kotaku that it is currently looking into the issue:
We're aware some users are experiencing issues playing Halo: Reach via Xbox One Backward Compatibility. The Xbox engineering team is currently looking into the issues and are working to address them.
We'll share more information as we receive it. Are you also facing issues with Halo: Reach on the Xbox One?