When comparing uScript + Unity3D vs Blacksmith 2D, the Slant community recommends Blacksmith 2D for most people. In the question“What are the best 2D game engines?” Blacksmith 2D is ranked 48th while uScript + Unity3D is ranked 97th. The most important reason people chose Blacksmith 2D is:
Automatically detects changes and updates bitmap cache. Allows to gain even more performance on heavy scenes and runs smoothly on old devices.
Specs
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Pros

Pro Automatically generates nodes for third-party script assets
uScript's nodes are a visual representation of actual code blocks, and it takes advantage of C#'s reflection capabilities to automatically create nodes for any scripts it finds in your project, regardless of the source. This makes it inherently compatible with pretty much everything.
Custom nodes can also be created by hand, for cases where the automatically created ones contain more elements than they actually need.

Pro Versatile flow diagram script model
Modeled after UDK's Kismet (the predecessor to UE4's Blueprint), uScript's scripts resemble flowcharts where each box represents a function or value, with connections between them representing program flow. This provides a better at-a-glance indication of game logic than a simple list of events, and makes complex behaviors easier to accomplish.

Pro Generates C# source code
Nodes are translated directly to C# files in your project. This is great for learning to code, and also for advanced users who can use uScript for fast prototyping and then further optimize the scripts if necessary.
Pro Cache as bitmap
Automatically detects changes and updates bitmap cache. Allows to gain even more performance on heavy scenes and runs smoothly on old devices.
Pro Most valuable when size matters
All engine code is written in ES6, fully GCC typed, allowing to eliminate all dead code from your app.
Pro Advanced scene graph and rendering pipeline
Dirty flag tracks scene changes and avoids unnecessary calculations and context calls. If no changes were made to the scene since last frame, no rendering will be done. Battery efficient.
Pro Good performance
According to the tests on the Github page, the performance is better than in Phaser!
Pro Good and clear source code
The source code is well commented and easy to understand.
Pro Super small build size
Super small build size through dead code elimination. The best for playable ads and Facebook Instant Games.
Cons

Con Not that easy to use
It's a lot more complicated compared to something like Playmaker. Same tasks take a lot more time.
Con Small community
The project is young, so the community is extremely small.
