Halo: Reach now runs pretty well on PC, courtesy of the recent improvements in Xenia Emulator's rendering techniques. While not quite as much of a household name as, say, PSX emulation is, Xenia has been making strides in emulating Xbox 360 as of late.
Whereas the previous builds of Xenia could only run Halo: Reach at a very low frame-rate, and with significant visual artefacts clogging up the screen, the latest version seemingly performs much more admirably.
Demonstrating weapon handling in what seems to be an empty multiplayer level, developers of Xenia have made a point of showcasing how stable it all is, because Halo: Reach barely used to boot not a few months back.
As per the video featured below, the only real graphical error to be found is the fact that firearms' muzzle flashes do not render for this or that reason. We also do not know what sort of hardware the developer is running, so that requires more looking into as well.
That said, Halo: Reach seems to perform really, really well on the latest build of Xenia, and since it's been reiterated numerous times already that the last generation of Halo games probably won't make its way to PC officially, this will have to do.