I believe that the killing of Soleimani has been both a positive and negative development.
On the positive side, it is undeniable that he was a war-monger, murderer of Syrians and Iraqis, and has had an influence in arming and empowering the Shiite militias in Iraq who are standing against the popular aspirations of the Iraqi population who have been demonstrating against the status quo. It can also be said that a considerable number of Iranians themselves are happy that he's gone, but cannot really openly verbalise their feelings due to the repression by the regime.
On the other hand, one cannot deny the negative aspects of his killing. The escalation of conflict between the US and Iran might take a more dangerous turn. One cannot refute the fact that Iran's leaders have been very rational (after all, they're faced with economic sanctions, domestic discontent and an increasingly angry US that is ready to strike against Iranian aggressions). So Iran definitely doesn't want to be bogged down in a war. However, in terms of the security of the US and allies in the region, we might expect more aggression from Iran whenever the US is weak in the region.