Here is a list of video game sequels that were ported direct to consoles/computers. . .

GEN = Sega Genesis
NES = Nintendo Entertainment System
SNES = Super Nintendo Entertainment System

Frogger II: Threeedeep! (1984, various)
Space Harrier 2 (1989, GEN)
Paperboy 2 (1991, GEN, NES, SNES)

Can you think of any others?

As to how good they were, I think the GEN version of Paperboy 2 outshines the two Nintendo ports since it also has voice samples added. All Paperboy 2 games, if you hit the female sunbather, results in a news article with the heading "HOSED BATHER FILES COMPLAINT!"

~Ben