This paper explores the impact of adaptivity of the plot and environment’s elements of serious games on user experience. Serious games, designed for educational and training purposes, benefit significantly from adaptive elements that tailor the gameplay to individual users’ needs, preferences, and skills. In the literature review, there are many researchers, who have developed serious games that adjust the educational content to the learner's level of knowledge. However, there is a notable lack of studies concerning the adaptivity of strictly game-related elements, like game’s environment elements or the game’s plot. This kind of adaptivity can enhances significantly the user satisfaction, having as result improvements on the educational outcomes. Regarding the above, this paper investigates how adaptivity in the plot and environment of a serious game enhance user satisfaction, likeability, motivation and learning outcomes. Through two case studies of adaptive serious games and their evaluation results, it is proven that adaptivity of the plot and/or the environmental elements of a serious game increase the user experience and satisfaction and contribute to the enhancement of learners’ educational performance. The findings suggest that adapting not only the educational content, but also strictly game-related elements, make serious games more ‘strong’ and effective tools for enhance engagement and advance knowledge.