The study takes a deeper look at the 2050 EU energy system. It builds upon a decarbonisation scenario developed in the earlier study METIS 2 – S6 which focusses on the EU electricity sector, and its interlinkage with the hydrogen and the heat sectors. While study S6 aimed for a cost-optimal dimensioning of the EU power system, the present study goes a step further and aims to derive more general conclusions. It sheds light on no-regret options towards the decarbonisation of the 2050 EU energy system, potential risks of technology lock-ins, and major drivers of uncertainty in energy system planning like system sensitivity to climate change and commodity prices. The analysis is complemented by an evaluation of the impact of an enhanced representation of hydrogen infrastructures and provides recommendations for a holistic energy system and infrastructure planning approach.