Final Fantasy III
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Random encounters are abundant around the map and players tend to bump into them, but it's a really good way to level up your characters. The job system complements the leveling up and if you are stuck in a rut (e.g. reduced to mini size vs pain-in-the-ass monsters), try changing jobs! In my opinion, the job system plays an important role in keeping things fresh, and I don't even sense the tedium normally associated with level grinding.
Combat is turn-based and it's pretty clear cut (to me at least), when compared to the series' Playstation counterparts. New players and RPG virgins shouldn't have a problem getting into (or fleeing from) combat, just keep in mind that combat comes along frequently (refer to previous paragraph)
Even with SD Gundam-styled character models, the game has a more mature tone compared to other similar RPGs on the Nintendo DS, such as Mario and Luigi: Partners in Time. And I actually favour this set up compared to that of the later, which had me in candy-coated, gum-drop flavoured anaphylaptic shock (metaphorically speaking) after 20 hours of play.
In any case, Final Fantasy III is a worthy addition to any Nintendo DS owner's library. It pretty much earned its place in mine.