Monogame is going to have the exact same drawbacks as Unity though (i.e. it is a GPU accelerated 3d engine as opposed to a blitting engine).
So too with Haxeflixel (at least for C++ targets, I forget how it handles it for AS3 targets).
Those arent the issues I'm referring to. Once you set the filtering and some other rendering setttings correctly that's not a big deal. It's more the issue of dealing with a huge tool meant for 3d, it's not that streamlined relative to other solutions. Purely my opinion of course.
As for level editors. You can always use DAME with whatever framework you use. Writing a custom exporter is trivial.
Of course if you want an integrated solution there's also game maker which is a 2D engine. Or Polycode (if it ever actually gets a v001 release).
Haxe is also I guess another interesting possibility. Although I've heard mixed reviews on its level of support. Also I just don't like AS much.

I tried it a year ago and it was brutal. I gave up.
I just tried it about 2 weeks ago and it was a world of difference, all platforms compiled with little setup required. They have a neat little command line tool for getting libraries you need (similar to the python one).
That said I've only done very small demos to play with it. I havent done a big enough project to get bitten in the ass by anything deeper in the library.