I don't think it's particularly good or bad. It might be good in a personal sense for me if Microsoft lets 'Toys for Bob' make a new Banjo Kazooie game, but overall the action is morally neutral.
However, 'is it legal' is the far more important question for the courts. Microsoft is a very large company, but despite this has very little foothold in gaming. They've finished third in every generation despite previous acquisitions and even with the two companies combined their shared revenue is nowhere close to 50% of the gaming market. It falls well short of any anti-monopoly statute and Activision-Blizzard wanted to be bought, they were not coerced into the deal. You'd have to show real and present harm to consumers, not the mere possibility of harm at some unknown point in the future, to block the deal legally.