If you’re the sort of gamer who carries their 3DS around town to pick up StreetPasses (and there are plenty of you out there!) you might have noticed that an awful lot of people are playing something called Monster Hunter 4 Ultimate. While Capcom’s Monster Hunter series has been a huge success in Japan since the release of the first game for the PlayStation 2, it’s only had a cult following here in the US. But with the latest addition to the series, which Capcom reported in April was the first Monster Hunter game to sell more than a million copies outside of Japan, it’s becoming a phenomenon here as well.

But what is it? And is it worth a look, or at the very least a demo download?

There are a few things about Monster Hunter 4 Ultimate – let’s just call it MH4U – that make it an unlikely candidate for the worldwide success of Nintendo-exclusive games like Pokémon or Super Smash Bros. For one, it’s not actually published by Nintendo. The series debuted on the PlayStation, but since the third iteration it’s been a Nintendo-exclusive series, and MH4U is only available on the 3DS. Unlike competitors Sony and Microsoft, third party games have rarely done as well as Nintendo’s own games on their systems.

It’s also not a kid-friendly game, and the most successful 3DS games have hinged on an appeal to both kids and adults. That’s not to say it’s grim or violent or oversexualized – it’s none of those things. The monsters are in the dragons-and-dinosaurs vein, the only violence is red splatter effects when you hit a monster (and the implication that you’re killing these animals and carving them up for parts, but nothing explicit), and there are no plate armor bikinis. There’s a lot that’s cute about it, not least the Palicoes – bipedal cats who serve as your sidekicks when you’re hunting solo. But the art style is realistic. When it’s over-the-top, it’s in a way that exaggerates without being cartoony, like comically large weapons that are still realistically detailed. Not even the Palicoes have the immediate, easily marketable cuteness of a chubby cartoon “monster”.

But what really limits its appeal to older players only is the gameplay. MH4U is an unforgiving, stat-heavy game that doesn’t hold your hand. It’s not as hard as the notorious Dark Souls games, but it’s still much harder than your average action RPG, and it may be the biggest challenge you’ll find for the 3DS. It’s a game that requires you to have at the very least a good online reference site or two bookmarked, if not a friend who’s been playing the series for a while. The tutorials give you a chance to try out each of the 12 different weapon types, explain how to do basic things like completing quests, and…that’s about it. It’s a nerd gamer’s game, geared toward people who genuinely enjoy getting into the minutiae of choosing the perfect armor set and spending a day farming the materials to make it, then doing it all again at the next level.

MH4U was clearly designed with the New 3DS in mind, taking full advantage of the faster processer and the new directional nub. Part of what kept the last game in the series so niche in the US was the importance of an add-on called the Circle Pad Pro, which any serious Japanese gamer owned but which only worked on the non-XL 3DS and had to be either imported or ordered through GameStop here. The new controls on the New 3DS mimic the Circle Pad Pro, but more importantly, MH4U’s controls are less dependent on that extra nub than MH3U’s were. The load times are noticeably longer on the older 3DS, and closing the game causes the entire system to go blank for several seconds, but it’s still perfectly playable.

While it might not have Pokémon’s broad appeal, Monster Hunter 4 Ultimate is a fun, rewarding game. The difficulty only makes it that much more of a thrill when you finally take down the Pink Rathian you’ve been throwing yourself at for hours. If you’re looking for a serious gamer’s game for the 3DS there are none better than the Monster Hunter series, and that’s something those of us outside Japan are finally learning.