The biggest reason not to buy Anthem is to wait for reviews. Yes, users and critics tested out the game over the last two weeks, but with updates coming quickly and another major update in the middle of March it is not going to be the same game.
This is especially important considering Anthem is a connected game where you need to play with other gamers and where you will need to see how the leveling goes, how weapon balancing handles and what happens with Bioware as the game arrives and players get more time with it.
Anthem also promises a better leveling system for weapons as the starting rifle ended up being more powerful than epic weapons you could acquire in the game.
It's best to wait another week or two to see not only how the next patch handles, but what BioWare is going to do to bring the game forward after this rough first month.