Age of Empires II: HD Edition has been out a little over a week, and has scarcely left the Top 5 best-selling titles on Steam since. It hasn't all been sunshine and mutton dinners with the polished-up classic, however, as the realities of getting such a dated engine to run on modern machines has caused some quirks. A patch is now available for beta opt-in that, notably, fixes framerate issues on higher-end machines.
The patch notes give very simple instructions on how to opt in: "To access the build, simply right click on Age of Empires II: HD Edition in your Steam library, select 'Properties' and then choose the 'Betas' tab. From there use the drop down to select 'performance' and steam should download the update automatically." Note that you will only be able to play multiplayer with others who have opted in to this build.
The notes speak of improvements that may boost your framerate "up to 50% on low end machines and up to 500% on the high end systems previously experiencing frame rate issues." My beefy work rig was one such system experiencing these issues, and while I haven't seen a 500% increase, anectodally, it runs noticeably smoother in larger battles than on the previous build. Other fixes focus on the new multiplayer functionality. It seems like Hidden Path is upholding the commitment not to actually mess with the balance or statistics of the game.
read the full patch notes on Steam