when the game starts a part the huge map (full size of the map: about 7 screens) is shown. The map itself is completely designed in the editor mapeditor.org (or in some comparable editor - if you know a good alternative to mapeditor.org - let me know) and loaded at runtime or at design time. The game engine should support loading of isometric maps (well, in worst case only orthogonal maps will be sufficient) both "tile layer" and "object layer" from mapeditor.org should be supported. Scrolling/performance of this map should be fast enough. The map and the game should be either in 2D (orthogonal map) or in 2.5D (isometric map)
Collision detection, "solid" objects. The mapeditor.org supports properies on tiles. Let say I assign a "solid" property to some tiles in editor. It should be easy to check this "solid" property in the game engine and implement kind of "solid" behavior, so the animanted sprites do not walk through the walls.
Collision detection - it should be easy to implement some custom functionality like "when sprite A is close to sprite B - call this function"
Showing "dialogs" or popup windows on top of the map - should be easy to implement.
Cross-browser audio support - (it is implemented quite well in construct 2 from scirra, so I'm looking for the comparable audio quality)
The game itself is a king of RPG but without fighting scenes and without huge "inventory". The main character just walking on the map, discovers some things, there are dialogs and sounds.
The functionality of this example from sprite.js http://batiste.dosimple.ch/sprite.js/tests/mapeditor/map_reader.html is very close to what I'm developing.