DKII on 04 April 2007
All I played was DQ8, and it was pretty much right in between Final Fantasy and Paper Mario in terms of difficulty/"hardcoreness", art style, and humor.
edit: Forgot to mention, the series is absolutely huge in Japan, to the point where they forbid launching it on weekdays 'cause everyone in the country would skip school that day to go get it. It's like bigger than Halo is in the US. Not sure if the spin-offs have the same success though, how is the DQ spinoff on the DS doing?
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