Mmmm....I'd put her above the likes of Rihanna, Britney et al, but perhaps below Amy W, who in my view had originality and an edge that made her stand out. To my mind, Adele's songs are too formulaic to be considered great, and her voice, whilst ok, is not great either. I like her look but I don't think that's important anyway as a musician. Her songs are bland but well-produced. I'd put her on my "perhaps later" pile of cds, but I can kind of understand her popularity. She has a kind of mass appeal, and perhaps that's enough. She writes her own songs and sings them from the heart. She has a personality that appeals.
Great though? No, not in my view anyway.