Not to melee Krogan?!
It's nothing more awesome to melee Krogan and it isn't that hard.
Just make sure you destroy it's armor first, give him distraction( Combat Drone), immobilize him( Cryo, Throw, Pull, Concussive Shot) or use Cloak and then just kick his ass!
Also Geth Shield Boost, Barrier and Fortification( if not Sentinel which has Tech Armor) special power helps in case you overestimate yourself.