So, in order to assist other families in keeping things calm while people hold carving knives in their hands, I'd like to offer some helpful hints in case anybody tries starting a Marvel VS DC debate as they pass the sweet potatoes.
Given how the Justice League movie just came out and is still in theaters, and in direct conflict with the current Thor Ragnarok for possible entertainment post-dinner, it's very likely that somebody is gonna talk smack about the lesser-received DC movie that is just too... grimdark about its own 'Verse.
So let's get this resolved by pointing out these key things:
1) Justice League (JL) isn't as bad as Batman V Superman.
Let's acknowledge the first film in this shared 'Verse was severely flawed. It focused so hard on setting up the Big Fight between Batman (Affleck) and Superman (Cavill) that it didn't do a good enough job fleshing out both characters to show how wrong Batman was to pick a fight against Clark, and how Superman wasn't more public in his need to atone for the damage caused in Man of Steel. Also, Eisenberg's version of Luthor - while a nice departure from the hamminess of Hackman/Spacey - was too creepy and too smarmy to be taken seriously as an Evil Genius threat. BVS didn't do as good a job it needed to fleshing out the backstory of their being other Metahumans in the 'Verse, just tossing up hints about Diana and about the others without giving better context. Forcing a lot of that exposition into Bruce's Knightmares was heavy-handed at best.
JL went a long way towards cleaning up a lot of that mess. It gave Bruce motivation towards repairing the mistakes he made fighting Clark, and made it clear he knows he was in the wrong. It only gave us one big sequence of "the team fighting each other" element that's expected in superhero team-ups - when the team tries to contain a resurrected Superman - but from then on it focused on the prime threat of Steppenwolf, a New God vanguard for the Big Bad of the DC Universe (DARKSEID).
What Justice League does best is establish solid foundation of a superhero team involving characters that were earlier hard to take seriously - Aquaman in particular becomes the brawling badass he's supposed to be from the comics - or were hard to establish as characters who can helm their own solo projects - future Aquaman and Flash movies should be easy sells to the public.
2) Gal Gadot continues to hit it out of the park as Wonder Woman.
You can even roll with the argument that she's not in this movie enough to make it more enjoyable. There are moments where the filmmakers could have gone off a side tangent to show how Diana as THE Amazonian Princess was becoming a potent symbolic figure to women and girls. Every minute Wonder Woman is on the screen is a minute you're paying attention, not just to the fight scenes but also to the emotional drama.
3) Affleck isn't perfect as Batman/Wayne, but he does nail one key element for the DCU to continue.
Affleck is a bit stiff as Bruce Wayne, not conveying much emotionally as though he's focusing too hard on how direct/professional he tries to be as both a billionaire and Batman.
Something that crops up in JL is how old his version of Wayne is. Granted, mid-40s in this day and age isn't old old, but in superhero years he's getting close to retirement. His post-fight with a revived Superman examined the bruises and scars his already 20-year fight against crime has left him, and the battle against Steppenwolf likely added more. Affleck does convince as a vigilante growing aware of how he's no longer meant for this, yet remaining aware that the War (with Darkseid on the way) isn't over.
This sets up the sequel hook for Bats own movie in this 'Verse, one that's still reportedly delayed by creative conflicts, but one that sets up the possibility of Batman's Final Battle (most likely against a Darkseid-empowered Joker) and paving the way towards Dick Grayson/Robin stepping into the role of Gotham's savior as Nightwing. It all depends on how they work it out (Psst: Warner Bros, get in touch, team me up with Kevin Smith and we'll nail out a Batman flick on this inside of six months).
4) There are genuinely funny bits.
Thanks to Ezra Miller as this 'Verse version of Flash - a raw rookie to superheroing, literally taking his first steps even though he can go as fast as lightning - there is humor aplenty from his actions and reactions. Speedsters are popular characters in superhero films - just look at the two different Quicksilvers for Marvel and X-men - in that they play with slow-motion effects with charm and child-like wonder. Flash is the same way: Watching him pull off simple things with just a touch of a finger at super-speed gets the audience laughing. And the bit where Flash rushes in to fight a revived and angry Supes - only to see Clark turn his attention on him at the same speed he is, highlighting how Superman is canonically as fast as the Flash - got some of the biggest laughs with the audience I was with.
5) It makes me miss City of Heroes all that much more.
Oh, sorry, this is me. Let's continue.
6) If you can't convince the others around the table about the merits of the Justice League movie, at least point out that The Last Jedi is coming out in three weeks (OMG) and that we all need to settle down and wait to go see that as a family/group. That should resolve all matters until later.
Just don't go talking rubbish about Hawk The Slayer.
Update: I kid you not! I did talk to my sister-in-law about Justice League today! I was right!