I’m excited by the release of Unreal Engine 4 (by Epic Games), and I figured I’d put a couple of my thoughts down in writing.
First, let me emphasize something that hasn’t been clear about this release: While UE4 uses a subscription model, a continued subscription is only required to get access to updates. Even if you cancel your subscription, you retain license to use & modify the engine. Don’t believe me? Read the second to last paragraph of section 3 in their EULA. You still have to (of course) follow the EULA and pay Epic 5% of your revenue from using UE4, even if you don’t have an active subscription. On the topic of the EULA: It is written in fairly accessible english. Yay!
I’ve seen people compare this release to Unity, and aside from differences in technology, one of the big things to note is that Unity keeps their source very close to their chest. If you’re a Unity developer, and Unity Technologies goes away or the Unity engine has limitations that you care about but they don’t, then you’re hosed unless you go the route of getting a custom source license (which I’d guess isn’t cheap). You have no source access, so you cannot easily remove those limitations, and you cannot add support for new (or old) platforms. The same thing was true for the Unreal Development Kit (UDK), which was the “non-AAA” license option for UE3, but for UE4 it looks like you’ll never be locked down like that.
Lastly, Epic is trying to encourage an open development process - both by them and by their licensees. That’s pretty cool - I cringe when I think about how many different times the same things have likely been implemented / fixed in the Source engine, both by Valve’s licensees, but also Valve developers. Epic realizes that their advantage is not (mainly) their specific implementation, but the sheer amount of engineering effort that has been put into making UE4 what it is. If licensees actually contribute back, then that will further UE4.
Disclaimer: I don’t speak on behalf of Valve Software, and I have no association with Epic Games. I have not looked at the source of Unreal Engine 4 (yet).