WiiWare:
Megaman 9 - 9
World of Goo - 10
DSiWare
Art Style Picopict - 9
DQ Wars - 8
Virtual Console:
Super Metroid - 10
Sin and Punishment - 9
Super Castlevania IV - 9
Super Mario RPG - 9
Secret of Mana - 10
Zelda MM - 10
Paper Mario - 9
Shining Force - 9
Gunstar Heroes - 9
DKC 2 - 9
Ogre Battle 64 - 10
PSN:
Braid - 8
Marvel vs Capcom 2 - 9
Overall, I would rank download services like this:
WiiWare/Virtual Console - 10/10
PSN - 8/10
DSiWare - 6/10