When comparing ImpactJS vs PlayMaker + Unity3D, the Slant community recommends ImpactJS for most people. In the question“What are the best 2D game engines?” ImpactJS is ranked 57th while PlayMaker + Unity3D is ranked 77th. The most important reason people chose ImpactJS is:
ImpactJS has an active user community that busily produces tremendous resources including videos, books, tutorials, walkthroughs and more. There are also comprehensive class documentation available.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Extensive documentation available to support development
ImpactJS has an active user community that busily produces tremendous resources including videos, books, tutorials, walkthroughs and more. There are also comprehensive class documentation available.
Pro Excellent collision detection system
Impact provides 2 types of collision detection; static and dynamic collisions. Both of which are easily integrated into game development.
Pro Extendable
Many plugins are available, including one called Impact++ which adds features like pathfinding and dynamic lighting.
Pro Level editor
Built-in map editor with support for tiling, collision layers, and actors.
Pro Optimized
Works with Box2d physics library, comes with all worthwhile elements for actors built in.
Pro Truly cross-platform allowing developers to build for anything
Extending the reach of a game developed with ImpactJS is easy due to the cross-platform nature the framework. There are Considerations around performance, resolution and audio, however all can be appropriately addressed when in development. Works in the browser via Canvas, even on mobile. Easily translatable into a packaged app.
Pro Easy to use
You'll need to put more time in learning Unity + Playmaker compared to something like GameSalad. But once get the hang of it and familiarize yourself with what it's possible to build with them, it's quite easy to use.
Pro Provides access to a huge list of assets through Asset Store
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 your game. The Asset Store has more than just music and art. It also has code and modules that can be added to your game such as unique lighting or GUI systems.
Pro Third party plugins support
A lot of third party plugins have support for Playmaker. Playmaker team also invest time to add support for a lot of third party plugins.

Pro Elegant state-based visual scripting
Instead of a single "if this then that" event list which can become very cluttered beyond the most basic behaviors, PlayMaker gives each object a list of states where only certain events are triggered, and performing an action also changes state.
This allows for a clean, simple visual representation which helps break complex logical structures into smaller pieces, making them easier to understand.

Pro Powerful
It basically can do same things as scripting in Unity.
Cons
Con Inactive
The last update was in 2014.
Con Cost of $99
While most HTML5 frameworks are offered as free open source projects, ImpactJS has a one time cost and no free option.
Con Comparatively high learning curve
Although C#, JavaScript, and Boo have extensive documentation available online, it could still be difficult to wrap your head around the library and Unity's component based system.
Con Limited tutorials
There are not a lot videos with Playmaker tutorials. Official text tutorials are also quite limited. Even not every action has a description on an official wiki.
Con Performance could be better for 2D
Performance can be a real issue with 2D games. Unity 3D is actually a 3D game engine, and drags a lot of overhead with it.
For mobile, one could never achieve the performance of more specialized 2D engines with Unity3D.
