Each of the 64 cores can independently run arbitrary C/C++ code, which is much more flexible than a GPU. Each core has 32KB of local memory, which can also be accessed by the other cores, and there's 1GB of external memory too.
Specs: http://www.adapteva.com/products/silicon-devices/e64g401/
Architecture: http://www.adapteva.com/wp-content/uploads/2012/10/epiphany_...
SDK docs: http://www.adapteva.com/wp-content/uploads/2013/04/epiphany_...