"This curry is delicious."
The problem here is that おいしい does not specify a degree, but "delicious" does. In English, "delicious" is already a superlative for good/tasty (delicious = very good/very tasty), and for what I understood おいしい just means that something tastes good, is tasty or is even delicious (but doesn't always mean that something is good enough to be delicious).
So if おいしい = "good"/"tasty"/"delicious", とてもおいしい = "very good"/"very tasty" and "delicious" = "very good"/"very tasty", then it makes sense that とてもおいしい = "delicious".
Then, "very delicious" has another problem: it is redundant. As delicious is already a superlative, "very delicious" is not giving any more (semantic) information than "delicious", other than emphasizing how you feel about it, since it's the same as adding another "very" to "very good". The first "very" already contemplates the possibility of it being infinitely good, but you can add more "very"s for emphasis ("It's my favorite dish. It's very very very good"). That said, "very delicious" = "very very good", so as とてもおいしい can mean the same as "very good", putting just "delicious" should be fine and correct.
Sorry for such a long comment. I got a little lost in my own explanation, not knowing how to make my point in a straightforward way
これ is the pronoun, when you just use "this" as the actual subject of the sentence. In this one, you'd have to drop curry if you wanted to use it: これはおいしいです = "this is delicious". この is the determiner, it needs another noun following it because it doesn't stand on its own, hence "this curry" = このカレー.