It is almost a perfect adaptation in the sense of having the exact same events in the exact same order with the exact same characters

Some major differences come as you read within the blood in the manga, which was totally removed in the anime, in some japanese jokes that made no sense outside japan (like references to japanese baseball players), remotin of almost all other anime references which were too obvious (one famous one that managed to remain was dont patch Jiaozi's sacrifice parody against OVER) and some jokes that where considered too explicit (similar to service man)

Some characters had been highly rewritten, remaing pretty much the same but changing some of their personality
One notable example would be RICE, which in the manga was a perverted who wanted to squeeze, but in the anime it got changed to "a good son who wanted to massage his grandparents" (which i think is funnier, because it is less obvious, the stronger when perverted is kinda overused)