The adjective great has many uses and meanings. But you are correct to use it in the sentence. This use/meaning means "important; highly significant or consequential". So, you are correct. Look at the following link and especially definition number 7.
If you click on the Thesaurus, you will see many synonyms (words with a similar meaning).
Look at the list with the title "Big League, adjective important" and you will see synonyms such as "critical. crucial, serious, important".
These are the words that describe the "problems".
God bless the people of the Ukraine.