5. Grand Theft Auto: Chinatown Wars
Like Halo, GTA's not a franchise that you'd regularly associated with the term 'underrated', but just try releasing anything on Sony's severely under-supported PSP - it's a recipe for disaster. Chinatown Wars actually first released on 3DS and came to PSP later, its big innovation being an assortment of touch-based minigames that tied thematically into you being the son of a Triad boss looking for revenge. You'd do everything from draw tattoos to unscrew car radios with the touch screen, and although the PSP version had to lose this control scheme, it did return for the iOS and Android releases. Chinatown Wars mostly fell apart outside of Nintendo fans initially whooping for joy that they had 'a GTA' on their system because Sony just didn't push it whatsoever. It didn't sell, it didn't chart - and it remains the only GTA that almost everyone who still identifies as a GTA fan haven't played. Oh, and on the iPhone/Touch version you can import your own custom soundtrack, just for kicks. Take that, GTA V!