SpecsUpdate
Question Ranking
Pros
Pro Free and fully open source
The entire engine is open source and makes use of other open source libraries. Source code is licensed under MIT and available on GitHub.
Pro In constant active development
Bugs are usually fixed that same day. Core devs are very active on forums. New features are always being worked on. HTML5, DirectX11, and OpenGL3.1 support have recently been added. (as of 4/15/15)
Pro Very high code quality
Urho3D is written in a modular and super-clean way, so that it can be integrated into the other parts of your game seamlessly.
Pro Good 3D level editor
Pro Fat-free codebase
Only use what you need.
Pro Includes a lot of samples
There are a lot of sample projects included with the engine for both C++ and Angelscript. They are mostly very simple applications built to demonstrate the engines capabilities and features.
Pro Does not require an editor to get going
Pro Small turnaround times while developing
Builds are quite fast, aids in rapid development.
Pro Good documentation
The documentation for Urho3D can be split in two parts: auto-generated from class references and documentation written to cover the various aspects, features and systems of the engine. The written documentation is pretty good. It covers most of the aspects of the engine in clear and understandable English.
Pro Unofficial Oculus Rift support
Information on enabling OR support can be found here.
Cons
Con Little documentation and small community
There are some high-level design docs and a bunch of examples, but code is poorly commented and nothing much more can be found.
Con May be a bit hard to get started
To install Urho3D you need to get the archive from GitHub (be careful to download the master branch) and extract it. After that, you need to compile the engine with CMake. If all the dependencies are installed, then it should be a straightforward process, otherwise you will need to track down and install all the missing dependencies.
For people who don't have much experience with CMake this whole process may seem a bit like magic. For people who do have experience with CMake, the whole installation will be relatively easy.
Con The UI can be hard on the eyes
Urho3D's UI could cause eye strain.