"Este problema es de gran importancia."
Translation:This problem is of great importance.
A lot of common words that end in -ma come from Greek and are masculine.
el problema, el sistema, el idioma, el poema, etc...
You could say it any number of ways, but it's best to do the most literal translation possible in order to avoid any chance of changing the meaning. Also, when you do a literal translation, you're more immersed in Spanish and will learn it quicker by thinking in terms of the exact Spanish phrase rather than changing it around. IMHO.
Context of the sentence likely impacts how you would translate it. For instance, the more formal way "This problem is of great importance" or similarly "This is a problem of great importance" are the types of phrase constructions that very official speeches, interviews, or documents might have.
But in essence, you are saying the same thing -- the difference is either simply of colloquial or formal variety.