Just played Rallisport Challenge 2 on the original Xbox. With the OSSC, the right component cables and a softmoded PAL machine displaying 480p, it looks insanely good for a 15 year-old game ! Soul Calibur 2 also looks gorgeous in 720p, so that would count as well.
Oh, and there's also Ninja Gaiden, Panzer Dragoon Orta, DOA 3, Outrun 2, Splinter Cell CT (showed in the video), they still look fantastic. God bless the original, ugly, fatass Xbox !
Games with strong art direction also age very well : TF2 as showed in the vid, but also Zelda Wind Waker, SMT : Nocturne or Jet Set Radio. I now cringe at my young self for not liking cell-shading at the time.