SCRAM makes Half-Life more difficult. To balance the difficulty, SCRAM adds goals and rewards in each Half-Life map. The core Half-Life game is intact in SCRAM. You'll be late to the lab again, relive the resonance cascade, and get ahold of a trusty crowbar. You'll reminisce with soldiers as they send bullets in your general direction. You'll get to file for comp time as soon as you get back from Xen. But this time enemies are tougher. Smarter. Faster. Deadlier. To survive you might come to depend on reaching the 3 lambda nuclei scattered in each level. Find one and you might be rewarded - find two or all three and you'll definitely get a nice gift at the end of the level. Determination and exploration are key to reaching the lambda nuclei. That and being really good at jumping.
This video demonstrates how the optional reward system works in SCRAM. Find one lambda and you might be rewarded at the end of the map; find two or all three and you're certain to get a reward. These rewards are available in each and every map, from stepping off the tram until meeting the G-man at the end.