When comparing Genome2D vs BlitzMax, the Slant community recommends Genome2D for most people. In the question“What are the best 2D game engines?” Genome2D is ranked 47th while BlitzMax is ranked 52nd. The most important reason people chose Genome2D is:
It's the fastest gpu-based framework out there for flash. It's beautifully optimised. It has very low rendering latency, low level OpenGL calls that other tech simply cannot do (ie Unity) due to Stage3D, and thus can render a lot more data quicker
Specs
Ranked in these QuestionsQuestion Ranking
Pros

Pro Lightning fast
It's the fastest gpu-based framework out there for flash. It's beautifully optimised. It has very low rendering latency, low level OpenGL calls that other tech simply cannot do (ie Unity) due to Stage3D, and thus can render a lot more data quicker
Pro Cross-platform mobile, desktop and web
Supports Windows, Mac OS X, Linux, iOS, Android, Web and native Flash.
And with the HTML5 export, it also potentially supports development for the Wii U :)
Pro Haxe!
Haxe is a strictly typed programming language that saves development time but still compiles high performance executables, and can build for tons of different platforms (flash, c++, html5, java, c#, etc.)
Pro Access to direct draw features
Has access to direct draw features so you can make you own rendering structures (scene graphs etc).
Pro Automatic dynamic batching
Automatically batch geometries with dynamic batching techniques (by using constant buffers).
Pro Component based architecture
Pro Multi target
You can compile on Windows, Mac and Linux. Nothing to change. There are solutions to compile on the same machine for 2 targets.
Pro Modular
There are many modules to extend the features of the language: you can create PDF (via a Cairo module), or just download/upload files (via LibCurl), playing streaming sound (via BASS) and so on (databases, xml, xls...) User can create their own module (they could be written in plain BlitzMax)
Pro Easy syntax
Based on BASIC syntax. Supports OOP, collections (array, list and map)
Pro Stable language and source code
After many years the language it self is very stable. The packages contains the source code of ALL modules (excluding the source of the compiler).
Pro Easy to start, high productivity
BlitzMax is just ready after the installation. Open the IDE, write your code and just press F5 to see the results. You don't need to install other things to use the language. Of course if you want to change the language itself - or modules - you need to install MinGW or other libs, but guidelines are provided and easy to follow.
Pro Fast compiler
With comparison to the some of the other languages Blitzmax compiles source files fast enough.
Pro Compiles to native code
Good performance thanks to native code on each of the target platforms.
Pro Garbage collected language
The language is garbage collected in two modes: reference counting or using the Boehm-Demers-Weiser conservative garbage collector.
Pro GUI for apps
BlitzMax provides the MaxGUI modules that allow to build GUI desktop applications for Windows, Mac and Linux (FLTK or GTK via a module). You also could create your own 'gadgets'.
Pro Great community support
the forum is plenty of examples and solutions! Community is strong and still working, available for getting an hand
Pro BLIde
BLIde is an integrated development environment for Blitz Max, designed to work very close to the project file management performed by BlitzMax engine.
It’s inspired by the .NET IDE and some other great tools, It’s been designed for hobbyist and professional coders.
Cons
Con Lacks documentation
The API documentation is minimal, there's not many tutorials and the ones that are there are very small and only cover the basics. If you want to learn how to properly use it, you have to ask the community or read the source code and figure it out.
Con Not too many games to showcase it
Con Slow development rate
Con Outdated and abandoned
The author neglected BlitzMax and works on Monkey2.
Con No mobile targets
Only desktop targets available: Windows, MacOS, Linux.
