The Island of Dr. Moreau comes equipped with a few obstacles for us modern readers, but it isn't too hard of a read in the long haul. Perhaps the most difficult aspect of Wells' novel is the antiquated diction (that's English teacher speak for "very old word choice").
For example, at one point Prendick says he follows Montgomery "up the companion" (3.4). In Wells' day, ocean travel was far more common than now, so Victorian readers would have instantly known a companion to be a set of stairs or ladder on a ship. In our era of airplanes, we might need a dictionary to understand that Prendick isn't climbing up some guy Montgomery had with him.
And let's not forget that Wells studied zoology in college. So he sometimes throws down some big, beastly scientific terms like "deliquescing" (9.7). What? Did melting not sound sciency enough?
To be fair, though, these instances are few and far between, and Wells writes with an extraordinarily modern touch. His sentences aren't ink trails that run for miles and miles, his descriptions don't overburden with pounds of details, and the pacing is closer to a Hollywood blockbuster than a Victorian novel. Compared to other Victorian novelists (we're looking at you Henry James and Charles Dickens) it feels like Wells had the modern reader in mind while he wrote.