Well, for Dungeon Explorer, some of the hints about where to go next in your quest are in the text (granted, this doesn't happen too often and you can probably figure out most by trial - n - error). Otherwise, you'd only miss the anemic storyline. Of course, I say play the english-language version! I like following the story, however simple it is
.
For Nectaris, though, you're not missing anything (go
here for comparisons). The menu system / statistics displays are really basic, so that's not a problem. You can find a description of the weapons online (the game does have a nice built-in tutorial and guide for all weapons, but this is only used briefly, if at all, whilst you familiarize yourself with the game).
Dungeon Explorer - consider getting the NA version
Nectaris - get JP version