No Zoom. The lack of a zoom lens on the GT750E means that the only way to adjust image size is by moving the projector. This could become a minor annoyance for a portable projector you'll likely have to set up repeatedly in different locations.
Rainbow artifacts. Rainbow artifacts are potentially an issue for any single-chip DLP projector. More important, if you see the rainbows easily, you're more likely to find them annoying in a long game playing session or watching a movie than when watching a business presentation. With the GT750E I saw an occasional rainbow with data screens and saw them a little more often with video and games, but still not often enough to find them bothersome.
Unless you're both sensitive to the effect, as I am, and unwilling to accept seeing any rainbows at all, it's unlikely that you'll consider them a problem. To prove the point, I connected the GT750E to a FIOS box and spent a thoroughly enjoyable couple of hours watching movies in 3D, despite the occasional rainbow.
Doesn't include 3D Glasses. The GT750E doesn't come with 3D glasses, which means you'll have spend extra for them, at $70 to $100 each. Optoma says you can find the identical projector selling as the GT750 with one set of RF glasses. At $899, or $100 more than the GT750E, however, you won't save any money that way.
Somewhat ironically, the GT750E's tight focus on game playing makes it a good choice as a jack of all trades. By designing it to handle game images well, Optoma wound up with a projector that offers good image quality for both data and video too. And by adding a sound system that's good enough for games, it wound up with one that's also good enough for movies or business presentations with sound.
Being able to use the GT750E for data and video is a welcome extra, but the best reason to consider it is for its intended purpose, for game playing. The simple truth is that it's well designed for games, with good image quality, good audio, high enough brightness, support for both RF and DLP-Link 3D glasses, and fully 3D-ready. If you plan to play games, the GT750E belongs on your short list.