Melancon is not a classic closer in that he does not throw particularly hard. He averages just under 92 MPH on his 4-seam FB, but he only throws it about 10$ of the time. His workhorse pitch, which he throws about 70% of the time, is the cutter which he throws almost as hard at an average of 91.0 MPH. It's a great pitch that he can use to jam left-handed batters and work the outside corner on RH batters. His main secondary offering is a knuckle curve which also serves as a changeup at 81 MPH. All 3 pitches are at least above average in terms of effectiveness by Fangraphs rating with the Cutter being his most effective pitch and a definite plus offering.
By all measures, Melancon should be the shutdown closer the Giants sorely lacked last year, which should also stabilize the rest of the bullpen and allow Bruce Bochy to return to the more traditional bullpen roles he is comfortable with and bullpens seem to like. The only dark cloud on the horizon is that he might be nearing the end of the shelf life for his TJ surgery which occurred 8 years ago. If that were to happen off the bat, the Giants would be stuck with a large 4 year contract. They seem to be hoping they can get at least 2 good seasons out of him as he has an opt out after 2 years. The way the Giants front loaded the contract when you add in the bonus money makes you think their ideal scenario would be to get 2 great seasons out of him then let him opt out and take the TJ risk to some other team.