You can't copy the concept
I want that all be so simple and logical.
But she isn't.
We have billions good selling clones like: Social farms, Zumas, match 3 and much more...
Its works, but not always and not for every one.
Shit happens, its Real world =) even with cool games
p.s Also one more interesting and fast game http://www.warsow.net/
like quake 3 arena - totally free
but not lucky with popularity in best days shi have something like 200-500 online
and now shi almost totally dead.
Imho: shi so better then quake 3 arena in many ways, but seams no one care.