Red Faction Guerilla

I got the new Red Faction game on the 360 yesterday and played it for four hours straight. I really enjoyed the first level (Parker) but i found that once i ventured out into the rest of the game it became really hard to the point that for a while i was incapable of doing anything. Unlike in Assasin's Creed where the amount of security personel that stood in your way increased steadily as the game progressed, once i left Parker it seemed like every target was way too guarded right from the get go.

I haven't gotten very far in the game so i was wondering those of you who have played the game more is this me not playing the game correctly and making more work for myself or is this something i'm going to have to get used to?

Also, I'm currently playing on Normal should i consider moving to easy if my game experience doesn't change?