Legal in Massachusetts now, a shop 2.5 miles from my home was one of the first two in the Commonwealth to be authorized to sell recreational marijuana. It took many months for the state's Cannabis Control Commission to develop regulations, the final step being certification of two labs tasked with testing the "product" for safe use.
I haven't touched it since I quit at age 28 (now 59),though my wife of the same age still enjoys it. I buy it for her, as it has helped with some of her medical problems that led to her recently being accepted for for disability. I don't buy from that store though, the lines can be hours long and prices are twice what I pay from a reliable local source for high potency locally-grown stuff. Other friends and family who have tried it say it's as good or better than the store-bought.
I don't have any objection to it being legal, though do worry about those who are stupid enough to smoke & drive endangering other innocent folks. There's no reliable test for "under the influence" yet, though law enforcement does charge people with it and their evidence collected plus testimony and on-scene video can be convincing to a jury.
This industry is in its infancy nationwide, there will be many changes going forward.