Its pretty easy to level up, im at level 48 right now. About the shooting through walls, yeah thats not gonna happen since the room must be cleared first. Anything with a 7.62 round or higher can go through several walls actually, and a 5.56 will most likely go thru one or get stuck inside. I dont see why they made the saw seem so powerful in the game, it does not have near as much recoil and only fires 5.56 rounds, basically its a fully auto m16.
I would hate to be the team leader who gave the order to my heavy gunner to fire through the wall and have shot a friendly inside. Can we say Court Marshall?
Leveling up to me is great not to show off, but for the weapons/perks you unlock. The desert eagle is awesome, so is the m14 rifle.