Stalker: Shadow of Chernobyl → Army Warehouses
If you become a Freedom faction, you will no longer be allowed into the Bar without permission, and those who join the Duty faction will have difficulty crossing the border between the Warehouses and the Red Forest—the Freedom faction has a checkpoint there.
Helping the Freedom faction commander repel the Monolith attack is still worthwhile. This will teach you the habits of the stalker cultists. Now let's go through the Radar.
See also:
First Aid Kits: S.T.A.L.K.E.R.: Shadow of Chernobyl