Although it is true that one can find many of the features in Unity being offered by other engines, the crucial differences come from three main sources: community, programming language, and ethics.
  Unity has a highly engaged group of users and its forums are bursting with information and troubleshoot solutions. Community participation also plays a role in the Unity Assets Store,  a space the engine provides for users to share their creations-3D modeling of characters, backgrounds, mods etc- with each other for free or sell them for profit.
  The languages adopted by Unity are C# and JavaScript, promoting a level of software compatibility that would be difficult to achieve otherwise, and allowing users to make games that run virtually anywhere.
  But the greatest feature in Unity for independent developers and small studios is the no-royalties policy. Games using Unity don’t owe the engine anything and have total control over their earnings. This might seem like a given considering the engine is free, but that is not always the case.

Unreal -one of Unity’s main competitors- claims 5% of all profits made by a game using their technology. Even in-game purchases are considered part of  share, an attitude that led to a considerable shunning by smaller studios that depend on their earnings to continue in the market.
   CryEngine  on the other hand, aligns with Unity by refusing to charge royalties but has plenty of downsides.
It's programming language ( Lua ) isn't as widely adopted and limits the engine's games reach, another issue comes from the fact all downloadable content offered by them is charged using a membership system that starts at $50 per month.
  CryEngine's case is particularly interesting since it was once at the top of game developers preference, but has fallen from the grace due to its poor documentation and resources. The situation has reached the point where rumors that CryTek - the company behind it - won't survive long began to circulate, discouraging prospective users from adopting it.
Other problems with the engine  which are frequently brought up in discussion boards and by game-media are its slow updates and overall clumsy user-experience, that alienates those who aren’t already seasoned game-developers.
We put together the following chart for a quick visualization of the data regarding the three engines so you might see it more clearly: