Minecraft was written from the ground up. Writing their own engine in Java has been the subject of great debate because of how poorly optimized it is, how every update shattered the mod scene, or how much work it takes to port it to all the various iterations on all the various platforms.
Terraria was written in .NET using XNA and met with huge success. But they too have seen similar problems and have to use external dev houses to get the game onto other machines.
Starbound is custom built. They messed up so badly with their initial build that it took them almost a year between releases to even release an update.
Kerbal Space Program _does_ use Unity, but even they hit a wall of shame caused by using the engine in a 32-bit variety. Mods are much easier because the platform is written using a "standard" framework, but the game will implode if you require more memory than 32-bit can address.
There are also plenty of success stories (Prison Architect might be my favorite game to watch develop) but I think the more complex the basis for the game, the smarter it might be to start with something that's proven and work your way up from there.
This assumes you can just plug in the engine and all is well and good. Many of these engines are optimized for certain types of games and do not play well when bent against their will. There is a large cost of learning to utilize the engine and get the best performance out of it. You are also heavily committing yourself to something where it is possible a wall could be hit and there would be no way out of it. Moving away from one of these engines is very expensive and may involve re-writing the majority of the game. It is not something you want to decide lightly.
Terraria was written in .NET using XNA and met with huge success. But they too have seen similar problems and have to use external dev houses to get the game onto other machines.
Starbound is custom built. They messed up so badly with their initial build that it took them almost a year between releases to even release an update.
Kerbal Space Program _does_ use Unity, but even they hit a wall of shame caused by using the engine in a 32-bit variety. Mods are much easier because the platform is written using a "standard" framework, but the game will implode if you require more memory than 32-bit can address.
There are also plenty of success stories (Prison Architect might be my favorite game to watch develop) but I think the more complex the basis for the game, the smarter it might be to start with something that's proven and work your way up from there.