Engine building is the mechanism that produces the most 'aha' moments in my gaming. The moment when your engine turns over for the first time and produces more than you put in — when the cards are synergizing, the resources are flowing, the multipliers are stacking — is genuinely exciting in a way that most mechanisms cannot replicate.

Terraforming Mars is the purest engine builder at heavy weight. Wingspan is the best at medium weight. Wingspan's engine building is tightly constrained — three action types, clear bird interactions — which makes the moments when it accelerates feel more deliberately constructed.

The failure mode of engine building games is when the engine never coheres. Card draw randomness can prevent the necessary pieces from arriving. The best engine builders address this through drafting (Wingspan), market access (Ark Nova), or multiple viable engine types (Terraforming Mars). Games that leave you dependent on specific card draws without mitigation feel frustrating rather than challenging.