Congrats on Killzone 2! I only have around 45% on it.
I just need the Complete all combo's one for PoP and then I have the platinum. I did all the combo's but it did'nt unlock, I'll try it again later on a fresh playthrough.
X-Men is'nt too hard, you have to replay alot of the levels to find things you missed and to max out your skills. They don't carry over to Hard Mode (which is only unlocked when you beat the game on normal). So not that hard just time consuming.