Spy: In Polar base, put your back to the wall on the balcony (where mercs spawn), use your optic camo thermal suit and go invisible, it is hard for mercs to see you and they usually run right past you, run out and grab and SNAP! People NEVER think of this and it is SOOOO obvious and easy. If you can jump up and hang on the balcony, you can shimy over, shimy over to where you balcony looks over the part with the truck and dumpster, you can easily pull one off. You can also jump down on them from the huge building. Or you can go down the zipline from the big building and drop down while ziplining and POW!!! Also you can hide in the dumpster.
In the Warehouse, there are plenty of cool places to hide and kill, hang off the ledge where Mercs walk across and use A to pull one off if he is close above you. On the balcony there are things you can crawl up, once on top, you can drop down and SMACK! If you stand on the fence and use optic camo, you can jump on them unnoticed. When mercs camp in the room where door 2 is, you can hide in that hole and jump on him or down and grab him. If they try to run across to the other balcony, you can jump down on him from the ledge above you get on from climbing the pole where you spawn.
Splinter Cell will finally get Co-op mode. You will be able to do loads of new things, such as take bullets out of your ally. There will also be a new feature that will enable you to turn invisible for a short amount of time.