What have you been doing in the last/past few weeks?

- I've sbeen watching a couple of superhero films and a brilliant <something> film about Kenya.

1. Matched tense (What have you been doing? I have been doing...)
2. "couple of superhero films and a brilliant film" suggests that the superhero films were bad (i.e. not brilliant)
You need another point of contrast, e.g. "a couple of superhero films as well as a brilliant documentary" (the superhero films may have been brilliant too, but they weren't documentaries)

I havedn't realised how beautiful that country is.

Is I HAVEN'T REALISED correct?

Yes, but not in this context.

I haven't realized => I still don't realize
I hadn't realized => I didn't realize before, but now I realize