If you love a good dual joystick shooter then Crimsonland is the best choice on the Vita. The biggest problems are simply the lack of visual variety and the Vita's own issue with joystick precision, but other than that Crimsonland is a game well worth the price of admission.
Is it great to play solo? Perhaps the first 60 missions. I can attest to having fun despite the problems I noted, but it is definitely better to play with your friends afterwards, especially in Survival. BLAST ‘EM TO BITS!