Alternative endings
Bad Final: After disarming Demitov, neutralizes Barisov.
Good final: After disarming Demitov, neutralizes Denko in the past. Then, go and use the TMD on the portal.
Your own end: After disarming Demitov, neutralizes the two objectives.
Reference to lost
Raise the level of the TMD to the maximum of its capacity, then immediately break the window behind the improvement machine. Get in the duct to find the underground wheel of Lost.
BORAT reference
After getting the RLS-7, you will cross a bridge on foot. This bridge gives to another superior bridge where you will find several enemy soldiers fighting giant spots. Use the TMD on the other side of the bridge to return the boxes to your place in the room. Within them you will find a letter with a reference to the protagonist of the film BORAT.