[risos]

The pitch accent ShinTakuya mentioned is actually a huge part of why attaining a native-like Japanese accent is so hard. It's more than just individual words having an accent that can affect the meaning of the word.

There are rules for the pitch accent of conjugations of verbs and adjectives, rules for compound words, suffixes, prefixes and even a combined sentence level accent that changes depending on the accent of the word contained within that sentence.

And to wrap it up, there's exceptions to most of these rules. Not to mention that names of places and people have their own accent that, while one can gain an intuition for over time, are still something to be aware of.

Edit: There's also the fact that English doesn't have a pitch accent system, so it's harder for English speakers to acquire an unconscious understanding and production of the correct pitch accent than it would be for someone whose first language is Chinese. While Chinese's tones aren't as complicated as Japanese's pitch accent, the fact that Chinese speakers have to pay attention to the relative pitch of a phoneme gives them an advantage when listening to words in Japanese as they will be unconsciously aware that the pitch of a word is important and most likely reproduce it correctly without conscious effort.