Sonic's only real power is his ability to run really fast, right? So why does Robotnik build his base with such an open design? Instead of having bigass fields and long, straight corridors everywhere, places where Sonic has a natural advantage, why not mix it up? Litter the outside of the base with loose irregular rocks and metal caltrops. Make the inside all switchback corridors and compact rooms with very tiny entrances. Don't waste robots and robot ammo covering wide angles of approach, just funnel Sonic into a series of tightly controlled chokepoints and concentrate your firepower on those. Maybe throw some landmines down, too. Too easy.