Enemies that are not Bosses can be killed with the ice pick; it just takes one hit to kill them. After about a second you will hear the sound of the ice pick breaking their spine.
If you want to control your Spiderbot, then use the icepick.
You can use the Gravity Gun to turn off alarms from far away. If you are seen and the alarm goes off, just point it towards the red square and push it forward. This will save you time dealing with the NPCs. This is especially helpful when dealing with the invisible guys.
Go to the area after you face the man in the mech in the Riot level. Look up at the stained glass using the sniper scope. There are pictures of nude women on the glass.
The most effective technique is to slow down time and hit him with a full railgun shot; the alternate fire of the railgun; or the alternate fire of the shotgun. However, you must first disable his shield with an EMP grenade. Once done, you will do substantial damage. It will break into a intermission sequence and spiderbots will appear. Kill themm then resume fighting the general. If you have enough Bio Energy, repeat the previous tactic. If not, use the EMP, then the alternate fire of the railgun or shotgun. The shotgun is easier to hit him with, but does less damage. After you inflict more damage, walkers will appear. Destroy them with the method of your choosing (rocket launcher recommended). Then, once again resume the fight with the general. This is his last round -- spare no expense. Wear down or use an EMP on his shield, then kill him with massive fire power, or one of the alternate attacks of the railgun or shotgun.