We can definitely call Unreal Engine a reliable ass, always making things going. This really came into action with the 3rd iteration, which was used by quite a few titles, for example Dishonored, Gears of War or XCOM: Enemy Unknown springs into my mind. Quite a few teams got UE so far.

The past tense is intentional, because Epic has stepped up with an interesting concept: up to now, everyone could get a hold of Unreal Engine 4 for only $19 per month, but from now on, everyone can download it for free along with the entire C++ source code! If your product ends up getting 3000 dollars of revenue, from that point, you have to pay 5% of the gross revenue every quarter to Epic. „We succeed only when you succeed”. Fantasic idea. Tim Sweeney, the founder of Epic Games has announced his plan in this video: