" He is evil" is to buy into the Judeo-Christian set of values. To say what's "good" or "evil" requires a system of values, otherwise, they're floating abstractions. (I don't buy into it, obviously...though I don't buy into satanism, either.) But to say simply that Satan is evil is to show a lack of biblical history. Lucifer means "Lightbringer," Satan means "Adversary." If you read the Old testament, you learn that the serpent in the garden is not referred to as either. Satan appears in the story of Job, having a conversation with God, no less. That's because in Jewish tradition, Satan as adversary was an "employee" of God, so to speak (to simplify, I liken it to the role of Slugworth in WILLY WONKA, someone hired by the boss to test the resolve of those seeking the Golden Ticket.) To say that Satan is simply evil-notice that God gave Satan permission to torture Job to test his loyalty. Who's evil?
I'm not certain, but I don't think the Jews have a concept of Hell, either. You can see the differences between the old and new Testaments on this count. Lucifer as morningstar is an interesting case because of the reference to Jesus Christ Morningstar elsewhere. But in Isiaah, Lucifer as Morningstar may be referring to Nebuchadnezzer.The whole story of the angel's rebellion, well, Revalations was rather tacked on at the end, and was a "dream" of John as opposed to being presented as "history."
At any rate, if you think life on Earth is inherently evil, profit is evil, food is evil, pride is evil, etc., and that the garden was paradise and the afterlife of Heaven is all milk and honey and angels on clouds, then yeah, Satan is evil. If you however, think that man belongs on this world (as opposed to this planet, natch), has a right to exist, that the body is not a source of shame, that sex is good, and you take pride in your accomplishments, then the whole Christian ethic is what's really evil.