The way Draymond plays does not look impressive or fancy to many people, but he is very effective in everything he does.
Defensively, I see Draymond as an elite defender, at the same level with Kawhi. Both can guard all 5 positions but Kawhi has an edge on defending guards with better lateral quickness and Draymond can defend inside better with great athleticism despite being just 6'7".
Offensively, in terms of scoring, let's take 2 best players that you mentioned, Melo and Paul George. Draymond is not a shot creator or volume shooter, but when he did, he did it pretty well, 49% FG and 38.8% 3 pts per game, both higher than Melo's and Paul George's.
Play making wise, he does not have great speed, ankle breaking moves or flashy passing like PGs you mentioned but he is willing to pass the ball and often find the opening shooters. Of course he has 2 of the best shooters in the league in the team but he has done it really well right at the first season trying to be one of the main ball handlers with 7.4 assists per game. Having him as the other ball handler, it really helps out GSW offense and relieves some pressure on Curry.
All in all, he is a very effective player all around, he can share the loads of many positions on the court and I can see him improving any team in all aspects. On top of that, he can be the "heart and soul" of any team with his fighting spirit.
Care to elaborate?