When comparing HaxeFlixel vs Adventure Game Studio, the Slant community recommends Adventure Game Studio for most people. In the question“What are the best 2D game engines?” Adventure Game Studio is ranked 23rd while HaxeFlixel is ranked 24th. The most important reason people chose Adventure Game Studio is:
Good for newbie game creators. Can be used for prototyping: on several occasions was used to make a demo/experimental version before creating a final commercial product on different engine.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Powerful language
Haxe is a powerful, cross-platform and open source language.
Pro 75+ demos
All demos have included GitHub link, so you can learn from the examples
Pro Getting started guide
Has a starting guide for people who are completely new to HaxeFlixel; from installing Haxe to a beginner-friendly HaxeFlixel tutorial.
Pro Uses Haxe
(excerpt from source): To help you do this, the (Haxe) toolkit contains three main components:
the Haxe Language - a modern high-level, strictly typed programming language
the Haxe Standard Library - a complete cross-platform standard library
the Haxe Compiler - an incredibly fast cross-compiler
Pro Fully free
HaxeFlixel is fully free and open source.
Pro Hardware accelerated rendering on native platforms
Pro Active development community
(excerpt from source):
There is a multitude of channels to interact with the community:
Our google groups forums
#haxeflixel on IRC (freenode.net)
@HaxeFlixel on Twitter
The HaxeFlixel organization on GitHub
The HaxeFlixel page on IndieDB
Join our development chat on Slack[1]
HaxeFlixel group on Steam
Pro Powerful debugger overlay
You can watch variables, log (trace) messages, and check for memory/frame rate performance.
Pro Modelled after Flixel
But with considerable improvements -- the HaxeFlixel team are constantly working improving and fixing the HaxeFlixel API, as compared to the original Flixel which is no longer updated.
Pro Easy 2D game development
(Haxe)Flixel does a lot of things for you like tilemaps and collision detection, which makes it super easy to create 2D games.
Pro Outstanding community
The HaxeFlixel team and contributors are very active on Github and other community places (like Slack), and are usually able to respond to your questions within a day or two.

Pro Similar syntax to Actionscript 3
Haxe's syntax is similar to AS3, so Flash developers can transition to HaxeFlixel if they are familiar with AS3/Flixel.
Pro Excellent, robust API
The API has all of the features that you'd expect from a powerful engine without sacrificing organization and flexibility
Pro Cross Platform
The open source Flash API is powered by OpenFL, which allows you to compile to Windows, Mac, Linux, iOS, Android, and even major consoles (coming soon).
Pro Cross-platform IDE environment
On Windows, the IDE of choice is FlashDevelop, but if you're looking for cross-platform IDE (Windows/Mac/Linux), there's Sublime Text which includes a package for Haxe syntax highlighting, as well as auto-completion.
Pro Easy to learn tool
Good for newbie game creators. Can be used for prototyping: on several occasions was used to make a demo/experimental version before creating a final commercial product on different engine.
Pro Completely free and open source
AGS is licensed under Artistic License 2.0 and is completely free for use for creating both freeware and commercial games.
Pro Relatively well documented
Besides the manual there are multiple text and video tutorials and code samples written by community.
Pro Used for a number of high-profile commercial releases
Adventure Game Studio has been used to develop games such as "Resonance", "Blackwell" series, "Gemini Rue", "Primordia".
Pro Lots of assets available
An extensive library of game templates and script modules accumulated over years. You can construct a simple game in hours (if you know what you are doing).
Pro Friendly community
An old, big and active community which would support newcomers not only in learning basics of the engine, but can help with every aspect of game making (including art, voice acting, moral support, etc).
Cons
Con Small community
HaxeFlixel devs are not as large as (example) Unity devs, so the amount of support and exposure is limited.
Con Natively supports only 2D
2D only native support, 3D could be supported with plugins though.
Con Uses dated tech
Engine is based on the old technologies, which impose number of limitations and may cause problems on latest systems (level of annoyance varies depending on your priorities).
Con Graphics renderer is a bit dated
Graphics renderer is not well optimized for high-resolution games and complex effects.
Con No visual editor for scripts
You have to actually write all scripts yourself.
Con Development is slow
Further development of the engine is currently slow, done by only few people in their free time.
Con AGS Script isn't as full-featured as other scripting languages
Its own scripting language has lower syntax capabilities compared to modern script languages.
Con Assets cover almost exclusively adventure/quest genre
The features, script functions and game templates are very biased towards adventure/quest genre. The non-adventure games were made in AGS (2D shooters, platformers, turn-based strategies), but their development usually requires to write everything from scratch.
Con Workflow is closely coupled with the editor
Workflow is very tied to the editor and custom file formats, which can cause problems for bigger, more professional projects (interfering with source control, parallel development, automated builds, etc)
