A hack is someone paid to produce artwork on demand. In that sense, Rockwell was definitely a hack, because, well, that’s what he did for a living: drew what the SEP wanted. “Hack” and “great artist” aren’t mutually exclusive, although they often be so.
But I think he qualifies as talented illustrater/mediocre artist because, to my mind, great art includes ambiguities. Rockwell’s work (for the most part) is decidedly unambiguous – it’s realistic in presentation, and you know what you’re supposed to think or how you’re supposed to feel about any given piece.
That’s not a bad thing. He was a very successful illustrator, and a decent artist, and I can see why lots of people like his work and want to look at it over and over again.
Critics, who are ultimately (when they’re good) people who see a lot of whatever art form they’re criticizing, think about it in depth, and like the art form itself, will inevitably often have different opinions from the general public. Work that doesn’t challenge them, that doesn’t ask questions, that doesn’t give their interest something to coalesce around, won’t win flattering words.
Of course, sometimes critics miss stuff. Art is being reevaluated all the time, with stuff considered good losing luster and stuff considered bad gaining luster. Will Rockwell be reevaluated? I think he’s in the process, to some degree; I know there have been critical defenses of his work.
And it’s not like there’s a final answer. Time passes, tastes change, work gets re-re-reevaluated, and things fall in and out of favor. If there are Rockwell paintings around in 5000 years, people who see them then will have opinions about them that we can’t even guess. All any critic – or any viewer – can do is give his or her honest opinion.
My honest opinion: I like his work fine, but it doesn’t move me or prod me to think or give me questions to ponder. It doesn’t strike me as special. His vein of nostalgia will probably become less and less effective as time goes by, which means he’ll probably be mostly appreciated by people who like realistic illustration and those with a cultural anthropological bent.
Glad you like him, though.