Original Xbox >>>>>> Dreamcast
MS redefined gaming with the original Xbox. Games like Halo, TES Morrowind, Kotor and Fable would never have come to consoles without Xbox. The games I mentioned were far better than pretty much anything the Dreamcast offered (except Shenmue). I have always seen Dreamcast as an overrated platform. It's mostly remembered by the sad death it had and by representing the end of an era in gaming.