Reading and understanding video games & manga is more challenging in that the way the people speak in these situations is much more informal, i.e. lots of slang.

You won't be able to get to the latter without spending some time on the former because the grammatical structures in idiomatic Japanese are full of contractions that arise from the spoken language.

Just as an aside, if you actually spoke like a manga/game character, you'd definitely raise some eyebrows. Probably not in a good way ;)