The first issue is that although Mappy embeds the graphics in the FMP format, the XNA library for it won't actually read these - you need the original graphic file and need to know the row/column count of the Spritesheet. This in itself isn't a huge issue, but I can see a few people getting confused by this requirement - I know I was...
It doesn't seem to support Layers - this could be a fairly big issue if it doesn't - I need to confirm this. My game will use layers for putting on zones that can't be destroyed, for example.
Looking at the interface, it's very rudimentary - there's a host more functionality that could be added - it doesn't seem possible to gain access to the tilemap array itself, for example - and it's impossible to swap out tile graphics for individual tiles (eg: the source rect of the texture being used). I'd also like more control over how the map is drawn - such as being able to draw selective portions of it.
It does have a few nice features, such as being able to pull back which tiles are within a given screen rect.
It's a good start but acts more as a map viewer than something that I could drop in immediately and use for what I need. As it's open source I'll probably end up modifying it and either sending patches to the author or forking it out as a separate project at some point.
