I wouldn't say he's -nice-, but he's not bad or evil so.

he's not perfect, but one of the greatest wizard...harry said so too...whatever he is, he's awesome !!

He's on the good guys side, but that doesn't make him a good person.

"Nice" does not mean "Good."

Nice basically means pleasant or polite to be around. People who alter their words and behavior to be pleasing to others. Snape does NOT do this. While I think he's "good" in that there is compassion in him deep down and he definitely does the right thing for the right reasons in working for Dumbledore, he's definitely not a sweet person.

See here for more of a description for why "Good is not nice." link

He's a good man but he's not particularly nice.

Yeah ^

He's on the good side, but he wasn't a nice person. I agree with Tygers_Eye.