Sega have released the mighty Streets of Rage too which is great news. Hardened fans of the series always prefer the sequel but if you can't wait for that then this is the next best thing.
New Adventure Island is a fun little platformer if a bit basic. Legend of Kage is a Taito arcade game from 1985 when almost everything featured ninjas in it. It's fun for a while but not a huge classic particularly.
As ever here are the reviews:
Donkey Kong Country - SNES (1-2 players, 800 Wii Points)
Streets of Rage - Sega Genesis / Megadrive (1-2 players, 800 Wii Points)
New Adventure Island - TurboGrafx16 / PC Engine (1 player, 600 Wii Points)
The Legend of Kage - NES (1-2 players, 500 Wii Points)