As you may guess, it was Scorsese's The Gangs of New York with Leonardo DiCaprio, Daniel Day Lewis, Liam Neeson and Cameron Diasz.

I havedn't watched it before, though it is shown on TV now and agaithen.

The past perfect is needed because what you’re describing occurred in the past in relation to the point of time that you’re referencing. “I haven’t watched it before” implies that you have never, at the time of writing, watched the film.

I clearly remember that I'ved seen only the opening scene, where Irish bgandgs prepare for the battle with New York bgandgs, but I'ved never seen the whole movie.

The most charismatic character of the movie is Bill "The Butcher," played by Daniel Day Lewis.

He is a natural in playing bad ass, evil personcharacters.

Or “people.” “Persons” is only appropriate if you want to have a certain tone, since it sounds either dated (cf. “persons of quality”) or legalistic: https://dictionary.cambridge.org/us/grammar/british-grammar/person-persons-or-people

Well, I'd say, it was an awesome two hours I spent on the movie.

It cheered me up a lot, because I hadwas in a bad mood that day.

I don't watched movies a lot, but it's nice to watch one sometimes, especially some of those good movies from the past, which that you've missed for some reason.

I would also replace “missed” with “not watch,” as here it sounds like you’ve seen them before and just want to watch them again.

I should saythink it is a great movie.

The word "should" implies that you don't think it's actually a great movie, but from the rest of your text I have the impression that you actually do!

I clearly remember that I've seen only the opening scene, where Irish bands prepared for the battle with the New York bands, but I've never seen the whole movie.

I liked the atmosphere of the old New York as it's shown in the movie, but I understand it wasn't the best time and the best place to live.

He is a natural in playing bad ass, evil personcharacters.

Well, I'd say, it was an awesome two hours I spent on the movie.

It cheered me up a lot, because I had a bad mood that day.

I don't watched movies a lot, but it's nice to watch one sometimes, especially some of those good moviones from the past, which that you've missed for some reason.

Rephrased to sound a little more natural and to avoid repeating the noun "movies". Also fixed the small grammatical error.