Typically, people who voice that opinion of DT either haven't actually heard more than a few seconds of DT, if any at all, and are just parroting what they've heard other people say. With most of these people, you could play them Disappear or Hollow Years, and they'd still claim that it was a musical wank shred fest.
We live in an age where some people automatically associate skill and complexity with lack of emotion.
Edit: There's this hipster type guy who hangs out with one of my friends sometimes. He made those kinds of claims about DT. I put on To Live Forever one time without telling him who it was. He loved it. As soon as he found out it was DT, he immediately started finding fault with it.