However, perhaps one of the reasons we lack major AAA games on Linux is the lack of a AAA engines or dev platforms. Two of the bigger free options are Ogre3d and Irrlicht.
Ogre seems good for those with some coding knowledge who want to jumping into mid-level functionality. It allows for one to quickly develop a polished environment and with decent modern effects. However, sometimes it holds your hand too much to the point where more advanced functionality becomes difficult to implement: notably advanced collision detection and manual objects/terrain. Documentation rot may also be an issue if you're trying to use a newer version with older tutorials. Ogre3d is free and open-source.
Irrlicht, on the other hand, seems to offer flexibility, but definitely holds your hand less. This makes it somewhat more complicated for a mid-level coder to get down to business and see results quickly. Irrlicht is free and open-source
Unity — which targets more AAA game development — has increased Linux support more recently. While it still primarily focuses on Windows development, the producers do seem to recognise that Linux may be an increasingly viable option in the gaming market. Currently Linux desktop publishing is still in preview, but seems to be making good progress.
Lastly, the new kid on the (Linux) block. LeadWerks will be finishing their kickstarter soon, allowing for full Linux support (as well as additional features). Leadwerks is not a free solution, but the ~$100 price for backers won't break the bank. Leadwerks also offers source-code licenses according to their site.