Ranked in these QuestionsQuestion Ranking
Pro Good code completion
FlashDevelop's code completion is pretty good.
Pro First class support for Haxe development
Pro Excellent support for Actionscript 2 & 3 (Flash)
Although everyone claims Flash is dead, it's still quite useful for game developers due to its rapid compile and run times, as well as great debugging functionality with FlashDevelop.
Pro Good number of project templates
While it's project template system is not the best compared to it's competitors, it still is decent and is a good way to generate some boilerplate code.
Pro XML/HTML completion
Has XML/HTML completion aside from code completion.
Pro .NET Framework 2.0 application
It's windows only, but it has tremendous support from plugin developers and a dedicated team that's been developing it for close to 10 years.
Pro Source-control support (svn, git, mercurial)
Pro Great debugging
Pro Zen-coding for HTML
Pro SWF/SWC exploration
Pro Great projects compilation
Pro Decent code generation
Although the code generation can not be really called top-notch, it's decent and sufficient for most developers.
Con Windows only
FlashDevelop is for Windows only, it's not cross-platform.
Con Haxe debugging is in its infancy
Although FlashDevelop supports breakpoint debugging on Flashplayers, native Haxe applications (C++) can't be easily debugged within FlashDevelop.