check if the left side arm has come loose from the bolt/axle. The feeling is a slight wobble when pedaling on the left side, so it might be the reason you feel som play. I guess other reasons can be missing spacers or possibly blown bearings, dunno. This happened with my atlas crank and it got replaced under warrenty (upgraded to a xtr real cheap

) In terms of a new crank if it's not replaced under warrenty, get a xt 970 crank from chainreactioncycles or something. Pretty cheap, light, stiff, durable, looks goods, versatile.