C++ has definate advantages over C-Script. Its faster, and there are multiple ways of doing the same thing (there is probably more, but I wouldn't know what exactly). The disadvantage is the complexity. C++ is hard to learn on your own (at least it was for me) and there is a lot to it. C-Script can be self-taught within a few years. After four years of just doing this as a hobby I'm already at an intermediate stage where I can do quite abit on my own.
So my point goes along with what AlbertoT said. Any large game is possible, it will just take more work and more learning to do it because it will either require you to understand C++ or be able to use C-Script in complicated and creative ways.
I don't know C++ very well. The most I can do is simple math with cout << and cin >>. Not knowing C++ leaves me at a clear disadvantage because I find myself having to work my way around C-Script's deficiencies. As soon as it opens up as an elective for my college classes, I'm taking C++. my advice is to learn both languages so you can utilize 3dgs to its highest potential.
Not to mention that if you know C-Script, you will have an understanding of the syntax of C++, or if you know C++, you'll understand the syntax of C-Script. Both languages are very different, but the way they are set up is quite similar. they both use semi-colons (I hate those things
), they both us +=, -=, *=, /= operators, both use functions, and so on, so knowing one language will help with the other.
A side note on semi-colons: If you ever use ActionScript or JavaScript, use semicolons. They aren't required, but its good practice to get use to adding the damn things in. (I hate those things!
)