I'm sure that's true for the latest 1st person view shootem ups but when I can run the likes of Quake 2 and Unreal[1] at more than adequate frame rates in a VM installed instance of win2k SP4 on 4 year old hardware (admittedly using a dual core Athlon with 2 or 4 GB of DDR2 ram with the on board graphics adapter limited to a 64MB share of the system ram) in a Mint 14 host OS, I've got to say that virtualisation has made great strides even in this area.
Whether you'd get a playable game using the latest hardware with something like 'Call of Duty' I wouldn't like to say but I suspect it would likely to be possible if you forego some of the rendering features and throttle the resolution back to a more modest 1024 by
768. [1] These decade or so old games were installed primarily to test the VirtualBox video emulation driver performance to see just how hard things could be pushed. The winXP VM didn't perform quite so well in this regard but this was entirely unsurprising. However, the winXP VM did let me prove that it was possible to get a USB slide scanner working that didn't have win2k support despite the claim that it did.