I'm only fluent in English, and have made various efforts (some half-hearted) at learning Spanish and Japanese. Spanish barely counts since that was in high school at the time and I put no work into it. Japanese came along later when I was an adult and became far more interested in learning a foreign language.
After the second Mandarin class (I missed last week due to the LA trip), I notice that Mandarin feels a lot different. I mean that my jaw, lips, and mouth feel like they are moving in strange ways (compared to English, Spanish, and Japanese) just trying to get the pronounciation correct. But it is very interesting.
The class itself is OK, it is somewhere between just a conversational class (i.e. let's memorize these two dozen phrases) and a full language class (i.e. where study include grammar). Pinyin is still very difficult, because I see the letters and have to fight an ingrained English pronunciation that instantly comes to mind. In that respect the Japanese hiragana and katakana is easier to deal with, but then pronunciation in Japanese is a lot easier than Mandarin anyway, even when romanized.