You have only 3 factors to consider IMHO;

1) The game will add content over the next few years and eventually will end up about twice the price of what it is today. Buy now if you want to save money. With the success it has seen I expect a fully polished game will be coming.

2) If the financial aspect is not important to you, enjoy the many other great games out there and buy it later.

3) If you enjoy replayability, this game has random seeds that will always give you a new exploration challenge. Boss fights remain the same, but their locations and the trip to get there will always be different. For that reason you can get a few hundred hours in right now, then put it on the shelf for a year or two and come back later.