Raam can be killed by throwing grenades to him, scattering his Kryll shield, then pepper him with bullets. Once he come closer, run around him but stay on lighted areas otherwise you're Kryll food. Head to the turret/troika at the place where he first emerge, and plug him with bullets. The End.

just finish the game. wah! the ending is very hard to believe in real time, totally looks like CG!  

Insane difficulty is truly insane. Usually it only take one melee hit on a wretches and its dead, but in insane difficulty it requires 2 hits for it to be dead.

About the RAAM stage, actually there is a few ways to defeat him. More precisely, 2 ways.

1st way is to use the crossbow and sniper rifle. Fire the crossbow at him so that the Krylls will be blown away from him and expose his head to be snipe at. You can also take the chance to snipe his head when he sends the Krylls after you.

2nd way is to use the Troika gun at the back. If you successfully manage to get on it and there is no Locusts flying beside the train, no Krylls passing by (look at the sky), RAAM is pretty faraway, & RAAM did not send Krylls after you, the Troika will be safe to use and it would be a matter of seconds before he kneel down before you.

I would say using the Troika would be easy for Hardcore and Casual. However in Insane mode, you will almost get no chance to go near the Troika & even though you're on the Troika, it will take awhile to kill him with it plus the distraction mentioned in way 2.

But you guys missed out ghostdevice man... he the rambo of GoW, one shot kill two and then later one shot kill three...