A trailer cannot and should not encompass everything that is good about a game or everything in a game. The "more is more" approach is frequently a key indicator of a game developer making their own trailer. I totally understand the impulse; they've spent years working on their game, and they want to show everything they think is amazing about it. Ironically, showing more can make the trailer less interesting. Not only that, but a trailer that tries to cram everything in to me smells of insecurity.
What is "too much" for a trailer? Isn't that subjective? Is there a tipping point where a trailer would be better had it been 10 seconds shorter? 2 seconds shorter? I think how much is "too much" is dependent on the expectations a trailer gives the audience; this works differently for narrative trailers and gameplay trailers, so I'll break it down one at a time.
When we sit down to watch a narrative trailer we expect/hope to see just enough story to hook us so that we'll want to see the rest of it. This typically means story setup for the beginning, escalation in the middle, and then a montage of exciting images that may or may not be shots from the end of the game or movie. The trailers that escalate a great number of times in the middle are the ones that feel like too much.
Think of it this way: Have you ever had a friend who recommended a film to you, but told you too much of the plot?
I have a friend who gets really excited about movie recommendations. Frequently he'll start with the premise, which typically involves the first act, and maybe a bit of the second. If I'm intrigued I usually say something like: "Cool, I'll check it out." But sometimes he can't contain himself, and proceeds to tell me "and then... and then... and then..."
Everything he says after I expressed my interest is too much.
As soon as the audience is interested, and thinking to themselves: "That sounds cool, I wonder how this will resolve?" that's where you either stop or do a montage of clips with no story context.
Here's an example. Watch this trailer for "Call of Duty: Black Ops 4 Zombies - Voyage of Despair."
This trailer is quite long. Here are the order of events
Woman describes her father's studies getting her in trouble
Friends vow to find her father, and bring him back
There's some sort of supernatural magic happening
There are zombies
There's a connection between the magic and the boat
Everyone is fighting zombies
They use a magic staff, and have traveled back in time
They're fighting stuff in the past
Look at events 1 through 6. These all seem like they follow one story, but 7 throws a curveball that feels so disconnected from everything else, it feels like a spoiler. I don't know about you, but this sort of hard turn instantly gives me a "Uhhhhhh, what are you doing?" reaction, and I can hear in my head someone insisting the trailer include the time travel segment, lest they lose a ton of sales. I then also hear the editors' eyes roll upon hearing this. For more about trailers that just keep going, read my post about trailer spoilers.
Showing the segment in the past isn’t totally bad, but I feel like it would’ve worked better as just a small teaser at the end to say: “But wait, there is one more thing…” By teasing it, they could prompt a: “Wait, what???” reaction in the audience, whereas showing a lot of it will answer some of their questions about this completely different area.
The other form of game trailer that decides "more is more" is far more typical. This is the game trailer which features a lot of callouts to its list of features. Let me get this out of the way right now:
A trailer should not be a feature list made into a video.
The only exception to this is for DLC trailers that add new gameplay content. This is fine because the target audience are people already invested in the game, so they do want to see an excitingly cut list of new features coming to the game. For example, this trailer for Robocraft.
In my opinion, Graphics with text should be used sparingly, and should never be used in lieu of showing the features with good game capture. Text graphics should only be for things that cannot be shown in the trailer by any other means. For example, critic accolades, online/local multiplayer, creator pedigree title cards.
The risk a game runs by centering their trailer around a ton of feature list title cards is that it gets boring very quickly; this is because after the second or third gameplay feature title card you've set this expectation the trailer is going to list lots of features, none of which are terribly unique. Whenever I see a game trailer with lots of text graphics, my brain is looking for something unique. For example, what game does this feature list describe?
Variety of level environments
Power up items and upgrades
Procedurally generated levels
I can think of at LEAST three games that this list of features refer to, and making trailers with these title cards would do them a disservice and make them very boring.
The other thing lots of title cards or a "tell, not show" narrator tells me is: we're not going to trust you to figure out what we're showing. We're going to tell you, and explain every bit." This feels to me at worst like disrespecting the intelligence of the audience or just using the easiest method to get through a lot of material.
These trailers for Redeemer and Strange Brigade both fall victim to this sort of approach. My eyes/ears glaze over when I watch these because I think a trailer that chooses to tell me what I'm seeing, doesn't make as big an effort to make what I'm seeing communicate on its own.
As always, the unique story or gameplay is what's most important. Explore them both only as necessary, then let the audience fill in the blanks with all sorts of speculation. This says you respect their intelligence, and will keep them more engaged.