Motorstorm: Arctic Edge - not only did it go from PS3 down to PS2, people prefer to not even acknowledge that it exists
Tales of Symphonia: Dawn of the New World - worst lead character in a game ever. I liked the original, this one is worse in pretty much every way.
I can't really think of any more that were really bad without the 1st game being really bad too (like Deca Sports 2)