First of all, the finale was basically an hour of Arrow wiping Oliver’s slate clean for Season 6.
We can bet that Oliver will still face some of his old familiar bad guys in Season 6, but Slade Wilson is currently the only one of Oliver’s supervillains still among the living, and that bodes well for a fresh start.
Malcolm’s presumed death via landmine means that Oliver’s very first nemesis and the source of a lot of his trouble over the past 10 years is out of the picture, and Prometheus’ quite definitive death via bullet to the brain means that Oliver has endured the villain who basically embodied every single one of Oliver’s doubts and mistakes over the course of the series.