A friend game me this game for free, so I thought I would give it a try. He suggested Delta mode as I play a lot of games and he mentioned it's easy. He told me to be stealthy, like Splinter Cell.
I'm not sure what I'm missing, but this games seems very tough! I've already dropped it to Normal mode and it seems impossible to be "stealthy." The guys hear you walking while cloaked, when you fire you lose your cloak, and when you let it charge, which it needs all the time, they seem to spot you for a mile away! Is this just a tough game like Ninja Gaiden or what?
I like the idea of the game and want to give it a fair shot, but holy moly!!
I just started playing too. Remember to crouch when you have cloak up. And for when you get in those firefights remember that LB will activate the shield mode. It takes a while to get used to. The first level on Delta took me an hour and a half. The second was half that time. Remember that you don't have to kill everyone. Pick your battles. Most of the time they will just call in reinforcements anyway.
Stealth is actually extremely effective once you get used to it. As the previous poster said, make sure you are crouching while moving if near guys. It will make it so they don't hear you and your shield will also drain slower. When you need to recharge, just couch or lie down behind some cover. Breaking line of sight will allow you to recharge without being discovered.
Most importantly, firing while cloaked will completely drain your power and reveal yourself. However, if you line up your head shot, pop out of cloak before shooting, and immediately reapply your cloak, not only will you be able to pull off stealth kills, but you can do it in plain sight of other enemies and they won't see you. I've cleared entire sections like this pretty much right out in the open. Give it some getting used to and you'll get the hang of it. Good luck.
Oh, also I know this is probably obvious, but using a silencer attachment helps as well.