The most important feature of the HD27HDR, which sets it apart from the other similarly priced competition, is its ability to accept and display HDR images that use the HDR10 format; it does not support HLG or Dolby Vision HDR. Dolby charges a licensing fee for Dolby Vision, so it's no surprise that Optoma did not include it here. But there is no fee to implement HLG, which is becoming important for broadcast HDR, so I wish the HD27HDR supported it as well. As mentioned earlier, HDR is found only in UHD/4K content, which the projector accepts and downscales to 1080p. In addition, it can synthesize HDR images from SDR content.
Many experts say that projectors can't do "real" HDR, because there is simply too little light coming off the screen. For example, Dolby Vision projectors in Dolby Cinema venues achieve a peak brightness of 108 nits, which is twice the peak brightness of a conventional commercial-cinema projector but only a tenth or less of what many HDR-capable LED/LCD TVs can reach. So, most people say that HDR projectors are more properly called "extended dynamic range" or EDR. I'm fine with that distinction, though in my view, the image quality of such projectors is still clearly better than those that reproduce only SDR.
The HD27HDR is well-suited for video gaming as well. The input lag is specified at 16ms in Enhanced Gaming Mode, which is about the same as the lag measured for the HD143X in our review of that model. In general, an input lag of 55ms or less is acceptable, while a lag in the mid-30s is considered good. The HD27HDR's input lag of 16ms is awesome, which will greatly please serious gamers.
3D might be gone from new flat-panel TVs, but it's still going strong in projectors. The HD27HDR supports all 3D formats, including side-by-side at 1080i50/60 and 720p50/60, over-under at WUXGA24 (1920x1200 at 24 fps) and 720p50/60, and frame-packed at WUXGA24 and 720p50/60. Viewing 3D requires an optional RF transmitter and compatible active-shutter glasses. Optoma no longer offers these accessories, but you can easily find them online from companies like Xpand.
Happily, the HD27HDR offers ISF Day, Night, and 3D calibration modes. These modes let you—or a professional technician—calibrate the projector for optimum performance with ambient light, in the dark, and for 3D content. The ISF modes are normally locked so they can't be inadvertently tweaked; you need a special code to access them, which you can get from your dealer or calibrator. Of course, it's unlikely that someone will spend several hundred dollars to calibrate a projector they purchased for under $650, but if they do, these modes are important.
Like many home-entertainment projectors, the HD27HDR provides an onboard audio system with a built-in speaker and a 10-watt amplifier. This is handy if you want to use it where there is no external sound system, but it's only a single speaker, whereas some competitors offer stereo or even stereo with surround effects. In any case, it's undoubtedly a far cry from just about any outboard speaker. Fortunately, the projector offers an audio-output jack that sends the audio signal to a speaker system, which should give you much better sound quality.
One feature that's missing from the HD27HDR—and, to be fair, most other projectors—is a suite of built-in streaming apps that can be found in so-called smart TVs these days. Optoma and LG offer a few "smart projectors" with streaming apps, but this is still fairly rare. Of course, most folks get their online content from a streamer such as Roku or Amazon Fire TV, which can easily be used with the HD27HDR.