Sadly STO has an extreme nickel and dime approach. If you make a leveling mistake, you have to pay to fix it. In order to buy an item more than 10 mil credits, you have to pay 5 bucks to remove the cap. Not enough inventory space? (there isn't enough) You have to pay 4 dollars, 4 times, on 1 character to max space out. It doesn't even cross over to other chars. Not enough bank space? 3 bucks, 4 times, for 1 character. You can waste day after day slaving away getting dilithium ore to exchange for zen. But that's real fun, especially how illiberal it is with the ore and that you cannot refine more than 8k per day.
I consider STO to be one of the best examples of a good Free-to-Play system. Compare it to Star Wars: The Old Republic, and you'll see what I mean. STO is surprisingly generous with what you can do without paying.