If you could buy only ONE game in 2010...

[okr]

Zelda Wii

or (if Zelda won't be released in 2010, which is very likely):

The Last Guardian

or (if TLG won't be released in the west in 2010):

Golden Sun

or (if GS won't be released in the west in 2010, which is very likely):

Dragon Quest IX: Sentinels of the Starry Skies