I've been there several times and had many opportunities to roam in the city center. I've seen the city changing (at least between the riverfront and Campus Martius) for the better. Back in 2008 it was really scary to walk alone the streets of downtown... I initially hated the city (mainly due to long haul flight for 2-3 days of training... but the desolate downtown didn't warm my feelings). With time, I came to like it. I enjoyed walking down the riverfront towards Belle Island. Above all I was amazed by the buildings from the old good years of Detroit. Had a local colleague as a guide, so I know the downtown pretty well. Now in a different company, I don't think I will ever return there.
I hope the city continues its rebirth.