The original Shiren (the one this is a port and 'remix' of) was the second Mysterious Dungeon game, and is still considered one of the best. It represents a very well-thought out refinement of the formula seen in the first Torneko MD game, and exists before Chunsoft began to expand the formula in ways that might really be considered objectionable.
There are four MD games currently released in the US:
-Torneko for PSX was developed by Chunsoft, but is generally considered to be a less challenging game than Shiren
-Chocobo's Mysterious Dungeon (2) was not developed by Chunsoft
-Nightmare of Druaga has some notable fundamental differences in terms of gameplay design, and Chunsoft co-developed it with Arika and Matrix Software
-Pokemon Mystery Dungeon was developed by Chunsoft, but....well, it's Pokemon, and because of that it's focused on considerably different things than the Shiren series (the main game is much less challenging, there's more of a focus on party combat, items are only really important in the post-game dungeons)
Basically, Shiren is simply a purer, more focused game than the ones you've likely seen so far. Perhaps more than any other game I've ever seen, it forces you - and helps you - to get better at the game, to learn how to handle all the problems the game will throw at you, to figure out how to get the most out of your resources. It has a arcade-like mentality of struggling, dying, and struggling again - but in a way that's much less frustrating than the average shoot-em-up or such, partially because death doesn't mean a total end to your game (indeed, some of the subquests require you to die multiple times, which you likely will). The more you play the game, the more you will realize that situations that iniatially seemed unfair simply required a different kind of thinking. In many ways it's like almost like a puzzle game - one with a wonderful atmosphere and a charming musical score.
If you don't believe me, I strongly urge you to do the unthinkable and emulate the game with the AGTP translation patch. It is well, well worth it to sink at least an hour of your time into the game, to try and understand it on it's own terms instead of that of other dungeon crawlers/mysterious dungeon games you have played. It's pretty much a certifiable classic. (just make sure not to use save states - in addition to causing some notable game glitches, it just isn't the way the game should be played. seriously)
I will concede at this point that the DS version of the game has undergone some notable balance changes and tweaks, such as the ability to return to previous floors and other things. But it has also added some new and unpredictable enemies, and I believe the bonus dungeons (the real challenge of the game, where everything you learn is tested) have been made even more interesting. I certainly haven't heard anything bad about the game from importers, and I expect that to stay much the same in the US - aside from those people who stubbornly refuse to learn from their experiences in the game.