Eurogamer lists some games you really should try:
"It's been a while since we've done one of these and, since each new console generation usually results in older hardware being passed on and great software going cheap, it seems like a good excuse to have another dig around in the archives for some of the PS2 games that never really got a fair deal. The games that were maybe too innovative to stand out in an industry increasingly devoted to predictable franchise-building. The games that were deemed too weird, or were sunk by poor marketing. This, then, is not a list of the greatest PS2 games ever made, even though several here certainly deserve that praise. Many more are solid 7/10 efforts that fell by the wayside. All are recommended for adventurous souls with a taste for the eclectic."