I normally have a loose categorisation of quality of racing seasons (F1 or otherwise).
Category 1 is when there is a championship fight between at least two drivers of different teams, and at least 7 winners (meaning from 4 teams) throughout the year. This for me is the gold standard for F1. I sometimes call it "CART competitiveness" because it reflects the level of close competition in that series' heyday. Recent examples of this category are 2012, 2008 and 2003. With this level of competition, it's unlikely the races themselves will be that dull.
Category 2 is when there is a tight title battle, but other teams don't get a good look in and wins outside these are either rare or non-existent. The best of this category would be 2010, with five genuine title contenders, four in the hunt in the final race, but nobody else won at all. Other examples could be 2006, 2000 or 1998. I'm usually fairly happy with this.
Category 3 is when there's a decent title battle, but it's over before the final race. But there's still enough unpredictability to keep things a bit interesting. 2018, 2017 or 2005 drop into this category. They can be good seasons, but end with a bit of an anticlimax.
Category 4 is the teammate title battle. This is when one team is dominant, but their drivers are battling for the title so it keeps things interesting at the front. 2016, 2014, 1996 and 1988 can be used as examples of this. Not ideal, but at least the fight at the front will have an intensity to keep things interesing.
Category 5 is when there is a single driver and car combination that is just able to extend their title lead with no problem, but the races themselves throw up some surprise winners. This is a 2019, 2011 or 2001 type season. We usually know after a few races who will be champion, but at least the other drivers can take it in turns to keep some interest.
Category 6 is when a single driver dominates with no real hope of competition. The inevitability of their wins sucks the fun out of the battle at the front. 2020, 2004 and 2002 are the obvious examples. This is when you have to focus on the midfield to find some entertainment.
This is how I've categorised it today. It's a loose system, but roughly sticks to those ideals. If every season was my Cat. 1, I'd never be bored.