Hiragana and Katakana are pretty simple and straight-forward. As for Kanji, I haven't studied the Kanji to deeply, but to me it comes down to pattern recognition and memorization.
My wife is Thai, and I've been trying to learn the language on and off for a few years now. For me it's the complete opposite of Japanese difficulty-wise. The reading and writing part is straight forward once you learn the alphabet and the special rules. The part I have trouble with most is the speaking part since there are multiple pitches and using them correctly is important. For instance "khao khao" is white rice, "now" can mean either means either cold or disgusting. Luckily, if you don't speak or hear the pitch correctly, most of the time you can get by using context.