I see a lot about Esperanto being really European. Does this mean that Esperanto is really hard for Asian learners?
This article, "Esperanto as language and idea in China and Japan", seems to imply that it's not particularly hard to learn for non-Western speakers (see comment for full PDF version). In fact, in 1907 Chinese anarchists called for Chinese to be replaced by Eo, which they considered as the more suitable language.
I also do not know any Asian speakers of Eo; but then, living in the UK I do not know many Asians altogether. So it might well be a case of the 'bubble' you live in. Previously I had come across the notion that Chinese people especially liked Eo as it was free of any colonial associations which came with the other European languages.
It still seems to be taken more seriously in China than in most Western countries:
1910s: Esperanto is taught in state schools in the Republic of China, Samos, and Macedonia. (Today it is part of the curriculum of China, Hungary, and Bulgaria.) (https://en.wikipedia.org/wiki/History_of_Esperanto
Then there is also the question of what it means for a language to be hard. This is generally related to how different a foreign language is to your native one. My native language is German, so I have little difficulty learning English, Dutch, and even Swedish. But Korean, Japanese, and Chinese would be harder for me to learn, as they are very different in phonology, morphology, syntax, etc.
However, by that reasoning Eo should not be any harder to learn for non-Western speakers than any other Western language. On the contrary, due to its regularity it would be easier. Perhaps not as easy as for a native Western language speaker, but still easier for a non-Western language learner than learning English, French, or German.
"Too hard" is very subjective. As Oliver has already outlined, it is easier to learn Esperanto (for people that speak languages that don't share similarities with Indo-European languages) than it is to learn other Indo-European languages. Here is a very personal account of Zhu Xin (祝昕), who learnt Esperanto in five months. Claude Piron talks of the similarities between Esperanto and Chinese - the isolating qualities - in this article.
So we'd just come back to your definition of what "too hard" means. The vocabulary is mainly from Romance and Germanic languages. Certainly Chinese people that have previously learnt another Indo-European language will find the vocabulary easier to learn than those that haven't.
Esperanto should be more difficult for people who speak "non-European" languages, mainly non-romance languages. Generally, Asians had studied English during several years. Even if most of them cannot speak, or even understand English, they had learned the alphabet and many words.
Esperanto is more difficult for them, but not as difficult as if they had never tried to learn another language. If an "European" can learn Esperanto in 2 to 6 months, for an Asian could be nearer to one year.
I have spoken Esperanto in Japan, Korea, China, Vietnam, Hungary. I have not heard any complains, but most of them would say that Esperanto is much, much easier than English.
Esperanto might be tremendously easier than say English.
But it is narrowly modeled after European languages. Coincidentally maybe some features fit even better in non-European languages, but starting with the grammar with its article-adverb-adjective-noun-verb-accusative upto expressions "bonkora" = (literally) "goodhearted" it needs quite some abstraction of a non-European.
That narrow adherence can be seen in kio = "what".
Say, what you are thinking = Diru, kion vi pensas (subphrase) What are you thinking = Kion vi pensas? (question)