Source vs Skyline

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.

A growing community that is always helpful with dev response times averaging less then 24 hours. Often less than 12.

Skyline provides a straightforward drag and drop development environment that can be customized to suit individual preferences. Playing the game and animating the scene can be done from within the editor at any time.

Future versions will allow extending editor's functionality with plugins and offer an official way of trading custom plugins.

Skyline's commercial edition costs just £40, has no royalties or earning limitations and includes 2 activations per license purchase and a year of free updates.

Skyline can be run on a machine with 2GHz Dual Core CPU, 2GB of RAM and Nvidia's 9800 GT (or equivalent) GPU. While, obviously, higher specs are recommended, it's reasonable to expect around 60fps on small scenes with these specs.

The Terrain editor is easy to use and will include features such as hole cutting.
There is a differed lighting render for internal scenes, which makes creating multi light and beautiful/atmospheric scenes so much easier.

All the tools for the terrain are in one place such as placing road/paths, vegetation, billboards, and the settings are easy to locate and change.

Planned features include:
Hole cutting in terrain and
Terrain paging.

Making a game in the current top engines is hard work, making something small and basic in Skyline is not. Easy to learn drag an drop model placement and editing supplemented with easy to follow video's on forum make the process straightforward.

Including image based lighting.

A free version that's limited to non-commercial usage and lacks a few features is available.

Rendering of a water plane looks fantastic and is easily edited for different effects.

The schematic editor is designed to make it easier for non-programmers to create games.

Not much in it at the moment but is starting to grow and will continue to grow with an increase of users.

There are many additions to the engine that are on the road map such as multi threading and tree physics.
The feature list is constantly evolving with each user request and idea put forth.

Skyline has a custom editor that gives the user of making their own tools for use directly in the editor to develop their games. All the editors are made using the Qt Designer and programmed in lua inside the engine itself.

Open-Source Virtual Reality support is in development.

Shadow editor.
Weapon Class Editor.
Mesh Editor.
Advanced Mesh Editor.
GUI Editor.
Script Editor.
Environment Editor (volumetric clouds and day night cycle, lightening, ocean settings, height fog).
Particle Editor.
Path editor.
Schematic editor.
Navmesh editor.
Material editor.

The documentation is been rewritten and follows a structure like a course.
Introduction to > Level designer with examples > Artists

There is also video tutorials, video examples and video tutorial series been produced.

There are user created demo scenes, examples and more.

Making HUDs and GUIs has never been easier

Full PBR workflow, your not stuck to Secular or Metallic it has both

Can contact the Skyline developers and they will always respond and help as fast as they can.