too serious and trying to be very important

The problem with the book is that it sometimes descends into portentous philosophizing. 这本书的问题在于它有时陷入了自命不凡的高谈阔论。

Portentous events, statements, or signs are important because they show that something unpleasant is very likely to happen

The report contains numerous portentous references to a future environmental calamity. 报告里有很多地方预兆性地提到了将来的环境灾难。