I bought syndicate as soon as it was released and played it to death. I was so addicted.
You learn a massive amounr about how the enemy AI works and how to take advantage of it.
Some tips:
1) Enemy teams never develop attack weapons beyond the Uzi/long range by default. If you develop heavy assault weapons, in time so will they. It's much more fun to divert your funds into body upgrades and rely on stealing heavy weapons. Use the persuadertron to get a full cryo chamber early on, you can use the agents therein to store weapons. The first new weapon you find is always given to your R&D team so make sure you use it first. Subsequent finds are yours to keep, you just can't reload them. Considering this, make sure you punish territories that have a military bias so you are forced to redo them occasionally. Consider it a smash and grab raid for the hardware ;-)
2) Enemy agents will always hunt your least armed agent first or if equally equipped, hunt them in numerical order.
3) Enemy agents don't appear duly concerned seeing any other of your agents whilst you first / least armed is still alive. They will only react to another agent of yours if you shoot first.
4) Enemy agents occupy zero volume and have little concept of height :-D. If you put your first / least armed agent somewhere fairly inaccessible, but with a space underneath, all the activated enemy agents will congregate en-masse on the point beneath.
5) Where (4) is impossible to acheive, you can ensure all your guys carry sheilds. The enemy will pile onto your guys position after pointlessly shooting for a bit. You can then send #2 in to roast them. Strangely, your flamer (or indeed any weapon other than explosives) will never hurt your own guys.
6) The flamer is incapable of injuring an enemy. It is always 100% lethal. Coupling the above observation, you can wait for the enemy to pile up underneath your first / least armed agent, then send number 2 in and give them a lick of flame. As long as you hit them, they will all die, none of them will be able retaliate. Use of any other weapon is not recommended for this trick. 15 aggrivated enemy agents simultaneously firing on your man with shotguns at exactly the same time will kill you unless you have a sheild activated.
7) For many normal missions, a squad of 4 v3 agents, armed with 8 long range rifles apiece will wipe the floor with the enemy, still relying on shotguns/uzis. They will never even get within a screens distance of you :-)
Recently I played it to see how quickly I can complete it.
The atlantic Accelerator is an exception to the weaponry rules. They all come equipped with minuguns aplenty. However if you make note of points (2)-(6) you will see a way to do it without a single casualty on your own team.