Neither is grim seriousness. It was less bleak than Lord of the Rings.
Well, I was understanding the term "serious" to mostly mean "not comedic" in this context.
If we are interpreting it to mean stuff like dour, grim, slow, boring, bleak, etc., then of course that is different.
The Simonson stories like Beta Ray Bill, or Skurge's Last Stand, or the Surtur Saga were very high-energy, thrilling and emotionally resonant. They shook up the status quo for Thor at the time, and injected a sense of foreboding and impending danger (the foreshadowing of Surtur was particularly effective).
So, anyway, the point is just that they didn't rely heavily on comedy to be entertaining and exciting.
Not to say that the film being comedic is necessarily a bad choice. Maybe it will have a unique mixture of tones and feel epic at the right moments.
But just as a personal preference or opinion, it doesn't really surprise me that someone might be looking for an epic tone, rather than a mostly comedic one.