I think there are several things that make English intimidating for many people:
Phonology: English is a high-phoneme-count language, so it may have more phonemes than the mother tongue of the learner – a problem for the likes of Spanish and Japanese speakers. Combine this then with getting your textbook and facing…
Phonetics: The Biggie, for many, as in “How many &^%# ways can you pronounce the same &^%#characters and still be in the same &^%$# language?” What makes the a in “many” different from the a in “can”. What makes the cha- in “character” be different from that in “champion”; what makes the th in “those” different from the th in “Thor”? Why is “cooperative” different from “cooped”? When is the -ed pronounced in “Blessed”? Can you really pronounce “goat” as “fish”? Etc., etc. Concurrent with the variable phonetics, a stripped-down ortography where there are NO diacritical marks to clue you in on what you should pronounce how. And you have to struggle with the phonetics while you learn…
Vocabulary: part of the root of the problem – English has a huge vocabulary accreted from many, MANY many other languages throughout a thousand+ years, and sometimes the imported word was “anglified” in pronunciation and spelling, sometimes it was retained as-is, sometimes it was hobson-jobsonned into something else. No obvious system or rule.
Also, English is one of, if not THE, language most friendly to coining words on-the-fly and transforming sentence parts: See the above use of “hobson-jobsonned”. This can confuse speakers of a structured language where a verb is a verb is a verb. Speaking of which…
Assembly of Verb tenses: This one doesn’t seem nearly as hard, to the casual observer. However…
… having so few distinct forms of the root verb(write/writing/wrote/written) means that English calls on a heap of auxiliary verbs and sentence constructions to do what others may do with distinct tense forms (for instance Spanish, with 18 or so). Also lacking person declension (xcept for 3rd singular) means you always have to stick “I”, “You”“He”“We” in front of the verb, which to speakers of languages with person declension can be extremely awkward.
These are only a few. The fascinating thing is that, of course, they work in both directions. An English speaker could be just as flustered by the 18 verb tenses in Spanish, by tone accent in Cantonese, by the sch-/ch-/shch- phonemes in Russian, or by formal(upward) vs. formal(downward) vs. casual mode of address in Japanese.
Oh, Priceguy, ** Neurotik**, jovan? The Academia de la Lengua Española* dropped the mandatory classing of the digraphs ch- and ll- as separate letters 1994. Now it is optional to give them their own section in the dictionary. This caused much wailing and gnashing of teeth among intellectuals across the continents as it was viewed as a capitulation to Anglo Cultural Imperialism, but it was really more a realistic tactical retreat in the face of ASCII code
STILL, the rule, in modern Standard Written Spanish, remains that each digraph is to ALWAYS represent the same sound, ll- distinct from l-, and ch- distinct from “c” (“h” is just a placemarker letter in Spanish); c and g are always pronounced one way before a, o, and u, always another different one before e and i. Otherwise, T is always T, A is always A (kinda Randian).