To complete on delta the most difficult setting for Crysis. The following rules apply:
1) You cannot control vehicle mounted weapons while driving.
2) Enemies are hidden and are invisible on the map, forcing you to find them.
3) Enemies speak Korean, and it is hard to understand what they will do.
4) Enemies won't glow when they attack you.
5) You will have normal binoculars, meaning that enemies will not glow in your binoculars.
6) Your Nanosuit will heal you very slowly.
7) You will die faster when not in armor mode due to the very low healing rate.
8) You have no crosshair.
To finish on delta you need to play with stealth approach because being attacked by more than 2 enemies at the same time you get killed instantly. This approach also discourages the use of jeeps and other vehicles (but no tanks) because that makes you a big target and you die quickly.
The best solution is to move always in cloak and in the crouch position this gives 2 advantages: low target profile and slower cloak energy consumption. If the cloak energy depletes and you don't have cover just hold down the B button to lie down, in this position the enemy has trouble seeing you and in that time the energy recharges and than rinse and repeat the process.
Another great tip is to use LB to enable armour just before firing the gun in cloak mode makes the energy not disappear while firing the gun which actually happens if you don't switch to armour mode, than you can switch back to cloak mode immideately after killing the enemy. The best weapon to be used in the game is the FY71, when you get the sniper scope you can use it as cheap sniper, don't keep Scar gun because the ammo is very rare in the game but there is plenty of FY71 ammo.
Edit: There appears to be some big and annoying bugs in the game.
1) (If you are missing the TAC gun and don't know where to get it, read this) There is major bug in the final mission, when the island is nuked and you are instructed to go to the deck, before reaching the deck a bug appears if you stay in more than a few seconds in the lowest chamber of the deck when you run down the stairs, the scripts kicks in which appears admiral being attacked by the alien and he dies, if that happens after nuke and before getting TAC gun you need to reload last checkpoint or even restarting the whole level again.
2) Angelr1pper reported that there's a difficulty glitch that happened to him. He suggest that before starting a new game on delta, go to options first and then to new game and select delta again.