Gamification in Education has laid the foundations for the utilization of game-based mechanisms to nourish learners' inducements, curiosity and engagement, through active game-play experimentation, thence enhancing their problem solving, critical thinking, technical and employability skills. In this Paper, we commence by appraising how User Experience and users' perception of the usefulness, convenience, adaptability and efficacy of an educational product of interest may lead to an exemplary, usable, functional, desirable and user-friendly, User Experience Design, which may holistically improve Gamified Education. Our conceptualization is assessed upon our Case Study; a cross-platform, innovative authoring educational gamified learning system product, covering STEAM (Science-Technology-Engineering-Arts-Mathematics)-related material, funded by the Hellenic Republic Ministry of Development and Investments, howlearn. An extensive overview of its end users and interrelated Subsystems is introduced, upon which, an exhaustive User Research is employed, designating users' desires and needs, based on a sample of 156 learners and 23 instructors. We, subsequently, delineate the System's Personas and Empathy Maps. Thereupon, we prosecute its design phase: from Paper Wireframes and Digital Low-Fidelity Wireframes, to the conduction of a Usability Study (denoting the necessity for the design's refinement) and the formulation of the learning system's Digital Mockups and High-Fidelity Prototypes. We conclude that, accounting for Accessibility, User Experience Design Principles and Responsive Design Principles is imperative, so that the convenience and usability of the design solution are ensured, thus leading to the formation of a gamified, socially sustainable, multidimensional, inclusive educational learning system, advocating lifelong learning.