Source vs Unity 3D

Valve's official documentation website is great for newbies. It demonstrates the pros and cons of the engine (and since the website isn't maintained by Valve, but instead the community, the pros and cons are largely unbiased). There are also a number of pages dedicated to entities used within official Valve games and also community-made mods that were turned into full-fledged games by Valve. These pages explain the ins and outs of how most source programming works. There are also guides for Valve's tools which are both included in Source SDK and in any Valve-developed game.

Since it has precalculated lighting, this engine is great for low end PCs too.

You don't need to code your own door or ladder etc. You can pretty much use every entity used in Half-Life 2 yourself easily.

Of course you can program stuff into source but for level design only, source has a really easy input/output system for your level logic (e.g. doors, trigger when player walks into room...).

Source includes Source Filmmaker, a video capture and editing application.

Unity3D provides an exhaustive documentation where everything is given a full description supplied by a number of examples as well as video and text tutorials and live training sessions to understand the ins and outs of the engine. In addition there's an ever-growing community that can offer advice to help resolve any situations that may arise.

Along with the official Unity resources, there are many high quality (and often free) third party tutorials available.

The way the editor is structured, by setting scripts on objects, and the use of a high-level language, C#, makes it easy to learn.

For those developers who can't afford an artist, or aren't skilled enough to create their own art, Unity features an Asset Store full of a wide variety of free and paid assets that can be easily added to a game. The Asset Store has more than just music and art. It also has code and modules that can be added to games including unique lighting or GUI systems. It also has powerful asset management and attribute inspection.

Unity is a proven game engine. It is used by a wide range of developers - from small indies to triple-A companies such as Microsoft, Paradox, Square Enix and Sega.

Unity's modular system and usability allows for quickly developing a prototype of an idea. It has features like drag & drop editing, shaders, animation and other systems already in place to allow diving right into developing a game.

Great Community support through the Forums and Unity Answers.

The editor GUI is very powerful and intuitive. It allows pausing gameplay and manipulating the scene at any time as well as progress gameplay frame by frame. It also has powerful asset management and attribute inspection.

As long as the development company makes $100k or less, it can use the free version of Unity to release games.

You can use any C# IDE for it, but the ones tested which have Unity integration are:

• Microsoft Visual Studio
• MonoDevelop
• Visual Studio Code (much faster than VS, but a bit harder to set up for Unity development)
• JetBrains Rider (very fast, has lots of functionality and best Unity integration, but it is not free)

Unity provides a great state machine animation system called Mechanim allowing to separate animation from the model and assign the same animoations to different models.

Unity offers over 20 platforms for publishing including mobile, console, web, VR, and more.

Not tailored for specific types of games (like Unreal...), so it won't get in your way if you want to make something unique.

The built in standard shader in Unity 5 is incredibly optimized and supports PBS/PBR.

Unity runs very smoothly even on systems that are considered "weak" by today's standards.

Overall, a coherent engine with a rational approach. People who complain a lot about being forced to hack around it usually do not read the docs, like the one that describe orders of execution, or specific functions hooks and such. Some like to say it lacks raw power where people who are used to standard optimizations have no problem. For example It is not uncommon to encounter users who complain about low FPS but forgot to activate occlusion, flag static elements, activate animations culling, and so on. As for complaints about C#, people who are transitioning from C++ were already bad at C++ before being bad at C#. They often come from the PC world where the sheer power of today's machines is very forgiving compared to the platforms we had to develop for in the 80s~90s. One of their errors is for example to never read this doc.

ReactiveX,async/await, etc. .NET functions can be used in Unity.

GitHub has a lot of extensions.

Unity allows free mobile development. There are some limitations.