In November of last year when the Doom 3 (id Tech 4) code was released followed by the immediate announcement of ioDoom3 on the Icculus infrastructure, it provided a lot of hope that open-source games would soon begin using this newer id Software game engine rather than the much older id Tech 3 engine code. Unfortunately, there hasn't been much ioDoom3 activity as of late.
The ioDoom3 Git repository hasn't been touched in months, the mailing list hasn't seen a message since May, their Twitter doesn't see much in the way of original Tweets, the Wiki doesn't see activity, the forums aren't frequented, and the BugZilla isn't even really active.
This follow-on to the ioquake3 project just hasn't seen much activity in the past eleven months. Any major open-source games using it yet? Not yet.
A bit more active than the ioDoom3 project itself but still based upon the open-sourced id Tech 4 code-base is Oliver McFadden's Dante project, which mostly focused upon renderer improvements, and then Dhewm3. The id Tech 4 Dante has found support for EGL as an alternative to GLX, OpenGL ES support, a new GLSL back-end, and even Google Android support.
Outside of id Tech 4, when it comes to open-source games doing impressive things, two projects worth following are the DarkPlaces-based Xonotic and the Daemon-based Unvanquished.