German is tougher than other Romance languages at the beginning when you start learning because the words in German do not sound like any Romance language. German has three genders (masculine, feminine and neuter) but Romance languages only have two (masculine and feminine).
Generally speaking, German is not as complex as most Romance languages. Verbs, for instance, are much simpler in German than in the Romance languages.
If a neutral person (one that does not understand any language similar to Latin or German) is to learn German or any romance language (Spanish) , it might be difficult at first to learn German but German becomes a lot easier and Spanish become more complex.
The reason that German is harder to learn than other Romance languages such as Spanish and French is that the words are spoken and conjugated a lot different. The gender of words are hard to understand in German where in Spanish it can usually be determined by the ending of the word. Spanish words are usually smaller and more easier to pronounce as compared to German.
The romance languages such as French and Spanish are more commonly spoken throughout other places in the world especially the United States.The reason for this is that they easier to understand than German. All of the romance languages are nice but the bottom line is that German is harder to learn than say Spanish and French. While German has been around for a very long time, it is complex and the different elocution that comes with it makes it somewhat more difficult to learn as compared to some of the other romance languages.