[Tomisimo]

It depends on what your native language is, or your other exposure to languages, but yes, some languages are harder to learn than others. It all depends on language features in your target language (the one you're learning) that don't exist in your L1 (your native language).

The examples of Finnish and Mandarin are valid for English speakers at least. English doesn't have a very extensive case system, while Finnish does, making it hard. English doesn't use tone to distinguish between words, while Mandarin does, making it hard.

Spanish differs from English mainly in three points: verb conjugations, subjunctive mood and gender. However, in general these differences are "easier" for an English speaker to learn than the tone and case of Mandarin and Finnish, among other differences in these languages.

Just my $0.02.