I think 25€ is a reasonable asking price. That's like an hours pay if you're not from a third world country.
Emphasis on the ASKING part since it's not mandatory to pay to continue playing, it is a free to play game after all.
Also, if the newest expansions were free and the game had a sub fee of 1,99€ per month, none of you would be complaining. In fact, you'd probably be praising the content that Anet delivers for that price.