Multi-criteria decision analysis (MCDA) is well suited to address complex public policy problems but could benefit from new tools to involve many laypeople. Online information on specialized topics could be more engaging by including game elements. This paper reports an experiment that assessed a gamified interface to (1) inform laypeople about the objectives to consider in wastewater management decisions, (2) assist them in constructing range-based preferences, and (3) provide a positive experience. We measured the effects with (1) a knowledge pre- and posttest, (2) the elicited weights and a range sensitivity index, and (3) an experience questionnaire based on self-determination theory. Answers from 174 participants indicated that participants learnt about the objectives and constructed preferences in both the gamified and control treatments. However, in neither were weights sufficiently adjusted. Our gamification making the ranges salient did not help overcome this bias. Both treatments were experienced as neutral to positive, the gamified being more entertaining. We discuss implications: if gamification of tools for participatory decision-making is to be promoted, it requires further research. Range insensitivity remains an unresolved bias in MCDA.