I expressed some skepticism about the Asteroid Redirect Mission in my recent Space Review piece (while making a suggestion on how it might be improved). But I think it's fair to say my attitude toward that mission is mild compared to that of Paul Spudis, a lunar scientist whom I interviewed years ago. Spudis also has a pretty clear opinion about the idea of a human flyby of Mars.
Meanwhile, for those who think Mars is all that, here's Lee Billings arguing that the real scientific payoff is on Europa. (What I'm not clear about is whether the Monolith's "attempt no landing there" dictate applied only to human or also robotic missions.)