Can’t open a passage in Tomb of the Lost Adventurer

You need to get close to this opponent so that he swings his melee weapon at you.

When this happens scramble out of the way (Shift on PC w/ keyboard, B on Xbox controller or O on the PS3), this will leave him exposed and stationary for a short period of time, now is the moment to attack the target.

After a short time he will raise the shield again, so you might have to repeat this pattern a few times (if I remember correctly this first shield guy is also wearing armour, so requires more time than others that come later).

Later in the game you can obtain other options that make shield guys easier to deal with (counter melee attack built in to a scrambling-dodge, for example), but the basic strategy is the same - get close, force them to expose them self, counter attack.

I've completed the game on hard and played around with other difficulties.

The only differences appear to be:

• Quick time events are, er, quicker. You have less time to hit that one button.

• Damage done to you by enemies is higher - on hard a single rifle burst can kill you.

• Non head-shot damage appears to be lower.

On my hard playthough I fully upgraded all the guns and skills just before the point of no return (the game warns you when you reach it), but that was with all treasures found and all challenges complete.

On Xbox there don't appear to be any achievements related to difficulty.