Yes, you should pluralize “movie” in the first sentence, but “these are” and “they are” are practically interchangeable for the second sentence, which, by the way, should be punctuated with a colon and not by a period. Those two sentences should then read as follows:
“Rarely do I get disappointed with Korean movies. In fact, these are the ones I love watching the most:”
Now the question is, of course, why use the plural “movies” instead of the singular “movie”? Well, it’s obvious from the sense of your statement that you are making a value judgment about Korean movies in general, so the presumption is that you have watched a good number of them to be able to make that judgment. When you say, “Rarely do I get disappointed with a Korean movie,” it makes you sound so biased toward Korean movies as to imply that you won’t get disappointed with any Korean movie even if it so happens to be awfully bad. But then, as they say, movies are movies are movies—some are great, some are so-so, some are awful, and the rest are dismal. So why make an iffy statement way ahead of time that you won’t get disappointed with a Korean movie even if you haven’t seen it yet?
Having said that, let me point out that you can make that first sentence semantically and logically airtight by qualifying it with a timeframe, as in this example: “Rarely have I been disappointed with the Korean movies shown in 2011.”
As to your second question, the present perfect continuous is typically used with a duration adverbial phrase, as in this example: “I’ve been standing in the rain for ten minutes now.” The present perfect continuous doesn’t require a specific length of elapsed time, only the sense that the action has continued uninterrupted until the time of speaking.
In contrast, the simple present continuous denotes continuing action at the time of speaking, with no indication of when that action started and how long it might last, as in this example: “I’m standing in the rain.” It’s like a snapshot of a fleeting moment in time.
