We're giving this book a middling score on toughness because Lahiri's writing really isn't all that complicated. Sure, she can be really subtle and, if you're not careful, you might miss details that would give you some "aha!" moments.
But in general, her writing is simple and clear. It's not filled with obscure metaphors and symbols that you need to decipher; maybe just one or two in a given story. In fact, the only thing she really plays with is the timeframe (she likes using flashbacks). And history—you might need to beef up your knowledge of South Asian history. Even so, it's not all that difficult to follow her stories.
So why don't we just give the book a 1 or a 2? Because she's still "high literature," which means she's going to dig deep. You'll probably need to read each story at least once more to appreciate all the details and how they fit together to make the story tick and the characters believable.
Her stories are fairly short and quick. Give her stuff a shot: she's really the perfect introduction to "high lit" writing. Not to mention an inspiration to young authors everywhere. Most early reviewers of the book had things like this to say: "Indeed, Ms. Lahiri's prose is so eloquent and assured that the reader easily forgets that ''Interpreter of Maladies'' is a young writer's first book" (source).