Full disclosure: I don't follow draft prospects, I have no ability to evaluate them, and I don't know what names were available at any given point in the draft. All I have to offer here is vague and unhelpful generalities.
I wasn't a big fan of picking a RB in the first round, and in general terms I think teams regularly shoot themselves in the foot by doing that. For the Patriots in particular, it seemed like an especially odd choice because they have been so good at getting adequate or better production off the scrap heap at that position. The problems with RBs are numerous: propensity for injury, relatively short careers (and associated higher probability of holding out if they turn out to be good), and above all that relatively low on field value. 1,000 yards at 4.0 a pop is lauded as a good season for a RB, but it's pretty common to put up numbers like that while providing very little in the way of actual value.
The counterpoints are that Michel is a dual threat back, not just a runner, and he was picked at #31, which means the opportunity cost wasn't as high as a typical 1st round pick, but he'll still get that extra year of control (a big deal for a RB who, if good, will be massively overpaid by someone else in FA before falling off a cliff). Michel also seems like the kind of straightforward "hit a gap and go" runner who should be pretty good at getting consistently positive yardage and converting short yardage situations, the places where RBs can add real value for their teams.
If Michel can put up some Lewis/Gurley type dual threat seasons, he's probably worth the pick. If he can do a passable impression of 2010 Lawfirm with regards to hitting the right gaps quickly and protecting the ball, that pick will be a huge win for the team.