dragon quest 8 for the ps2 was the first of the series i played and i really enjoyed it.  i played dragon warrior 3 (i think its 3) for the gameboy color, and got about halfway then couldnt really play it cuz it felt like i was playing the same game.   then i started dragon quest 7 for the psx and barely made it to the second town cuz it felt too much like the other two.  now i know since they are the same series they should have some similarities, but the battle system hardly changed at least between the three games i played.  i ask this cuz ive been contemplating getting the one that just came out for the ds but idk if i should if its just gonna be like the rest.

DQ5 is way quite a bit different than 8. And is my favorite. 

DQ5 lets you pick your wife. etc. 30 years pass during the time of the game. And the plot is cuter with more emphasis on the story than 8. probably the cutest plot in a videogame for me that I've played (be that a good or bad thing).

I've only played 4,5,8,9... I like the older ones more (err sorta I played the DS 4 and 5). Haven't played 3 or 7.

DQ5 is  one of my favorite games... while the others are a ways down. In my opinion anyways.

Yes, they all have the same exact style of play and combat system. You could compare it to Pokemon games.

Yes, they are all awesome.

I've only played IV, V and IX.  I've imported VII, but haven't got round to playing it yet and will get VI when it is released.

I would say that despite all having pretty much the same battle system and style, IX can be seen as a departure for the series.  It has a large emphasis on co-operative multiplayer and has much more of a focus on post-game side quests.  I've put 85 hours into my copy and I've only scratched the surface of the game.  Basically, get DQIX.