The Pacers have a very nice team right now. However, they are still somewhat lacking in high end talent and on the defensive end. This trade helps patch up both of these holes in a major way. Mikal is an elite defender when he is not the number one offensive option, and he fills in as a number 3 excellently. This trade will give the Pacers a very long, versatile starting lineup, with Haliburton/Nembhard or Sheppard (if he develops well)/Bidges/Siakam/Turner. They would have shooters, defenders, playmakers, and ball handlers up and down the lineup. They move some of their younger prospects and picks, but this would make them a real contender in the East for a long time.
The Nets get some very nice young pieces in Walker and Neismith plus a nice amount of picks here.