Level of difficulty : BRUTAL.
It's brutal, but it's so common with roguelikes, I've used to it. You die, you go down to level 1 and lose all your items, if you haven't stored them in the storehouse. If you have a wifi connection, or friends with the same game, you can send a rescue request up to three times per adventure, so the situation is not as hopeless as with your average PC Rogue clones. Though with wifi... I find it the easiest to send a rescue request just before I go to sleep at night, so in the morning I find myself most likely to be revived. It can take hours to get a revival spell. You can also go for a rescue mission yourself if you feel like it, and if the rescuee is grateful enough, you might receive an item from him/her as a reward.
Considering that Shiren is a conversion of a game on SNES, it has aged gracefully. Without knowing it's history, I still wouldn't had complained about the graphics. They're typical 16-bit RPG graphics, sharp, colourful and simple. Monsters have the usual approach with abilities and so on, you can get poisoned, stunned... You know the deal if you've played even one japanese RPG in your life.
With wifi, you can access the leaderboards of the game, and submit your best scores to it as well. You'll soon find that you need tons of practice before you have a shot of entering your nickname to it...
You like Nethack? ADOM? Pokémon Mystery Dungeon? Izuna? Grab this for a real challenge.