Japanese is Subject-(wa)-object-(predicate), with verb terminator. You have wo and ga following direct and indirect objects; vocalized punctuation from ka and ne; and context-implied elements ("Run!" instead of "You run!" because no shit I mean you).
Japanese particles have no strong correlation to anything much in English. They are grammatically important words, vaguely similar in function to English prepositions. Sometimes particles might be like conjunctions (to is kinda like "and"), sometimes they might be like punctuation (ka on the end is a verbal question mark), sometimes they have no good translation (wa marks topic, or contrastive subject).
FWIW, wa is more often considered a topic marker than a subject marker. Samples:
Watashi wa gakk ni ikimasu.
I [topic] school to go. > I go to school. -- basic topic is "I", which fits as subject in the English.
Watashi wa unagi desu.
I [topic] eel is/am/are. > I am an eel. -- basic topic is "I", which definitely doesn't fit as subject in the English here. A proper translation would be more like:
As for me, it'll be the eel. > I'll have the eel. -- such as when asked for one's order at a restaurant.
The particle ga is closer to a subject marker in function. For instance, Watashi ga unagi desu could only be interpreted to mean "I am an eel." Meanwhile, ni is vaguely like indirect object.
And, as you note, Japanese is incredibly more context-dependent than English. Oftentimes, anything that can be omitted from a sentence will be omitted, particularly anything that is clear from context, that has been previously established in the text or conversation or what-have-you. This makes Japanese into English interpretation a real bitch -- your example of "no shit I mean XXX" can get really tricky. If you miss the first part of what someone says, and you've lost the thread, you're absolutely hosed. English grammatically demands a lot more context-providing words, even when we think we're omitting detail. He's going to the store could be rendered in Japanese as just Ikimasu (go/goes/going/will go), if the context allows -- we don't even have the gender of the subject here in Japanese, making it much harder to try to guess.
More on topic to the greater thread, I've studied both Mandarin and Japanese, and I found Mandarin *much* easier to wrap my head around. Mandarin is a kind of language called an analytic language -- words are pretty broken down, even more than English, with no inflectional endings like "-ing" or "-s" or "-ed" etc. for tense, and no differences in a single word for singular or plural, that kind of thing. It's very streamlined in some ways. The Mandarin word mi can mean "buy", or "bought", or "will buy", without the need for different tenses -- tense is supplied by context, such as adding in the word for "today" or "tomorrow".
Japanese, meanwhile, is a very synthetic language -- words are glommed together with other elements to express different things like active/passive and adjectives, or even basics like tense or social context. One fun example is highly infected verb-based forms in Japanese, like saserareyasukattanda, which means "it's the case that he/she/it/they was/were easily made to do [something]".
Social context in Japanese is very important, kinda like Spanish tú vs. usted or French tu vs. vous, only on steroids and totally whacked out. Just looking at tense and social context in Japanese, the English terms "go" or "will go" can be variously expressed by the Japanese iku ("go" when talking to friends or familiars; present and future tense in Japanese are generally the same), ikimasu ("go" when talking in less-familiar social contexts), mairimasu ("go" when talking to someone else about oneself in a formal context), irasshaimasu ("go' when talking about someone else in a formal context). Then there are different permutations of each of these for negatives (ikanai, ikimasen, mairimasen, irasshaimasen), past affirmatives (itta, ikimashita, mairimashita, irasshaimashita), past negatives (ikanakatta, ikimasen deshita, mairimasen deshita, irasshaimasen deshita). And depending on grammatical construction, the formal forms might instead be mairu, irassharu; mairanai, irassharanai; maitta, irasshatta; mairanakatta, irassharanakatta. And that's not getting into the fact that mairu and related forms can instead mean "come", and irassharu can mean "come" or even just "be".
Just using this "go" example, Mandarin is much easier: that whole grammatical construct in Mandarin can collapse down to just [bù] qù ([not] go).
As far as I'm concerned, Mandarin is the easier language.
