I'm going to fall a little out of the norm here, I think, but I'll add my two cents.
If the question is purely "How do you create a good first impression?" in terms of your game, then that answer is going to vary wildly depending on what your game actually is and who it is targeted toward as an audience.
These are, invariably, questions about "Marketing". As such, you can learn a lot about how to do that effectively by simply watching trailers for movies. Well... most trailers.
Is the movie an action movie? Guess what's in the trailer? A baseline set up of who the heroes are, who the villains are, the general motivation of both, and then it's like 2 minutes of action and one-liners. The more bombastic and funny, the better.
Is the movie a romance movie? Guess what's in the trailer? Who the romantic leads are, the premise behind how their relationship gets started, the set up for what is keeping them from "true happiness", and then just a bunch of scenes of them being romantic and contemplative and maybe sad.
Is the movie one of horror? The trailer is the basic set up for whatever you're meant to be afraid of, and then a lot of disturbing imagery and a few scares thrown in to give you a "sample" of what you can expect.
On and on.
This is typically pretty great marketing.
For me, video games need to rely on this same sort of presentation.
Who are the main characters? What is the premise of the game? Now show me what I can expect. If you have a demo, it needs to establish this stuff as well... except it needs to MAKE ME CARE about those things (which is why a lot of demos for games don't really translate to sold copies... Because the people who make the demos have no idea how to market anything, and aren't really giving you a good impression of their game that makes you care about what is going on).
Then, your game actually needs to match what that marketing is portraying. Especially in terms of pacing.
If you advertise your game as, "You're going to run around on the island and overthrow the warlord and blow up a lot of stuff in crazy ways!", then your game sort of needs to do that decently frequently. This is why Just Cause 2 was a ton of fun... and Just Cause 3 and 4 just... aren't. Just Cause 2 advertised itself as "You are blowing up stuff constantly and grappling all over the place and doing crazy stuff with the physics". The gameplay of Just Cause 2 is "You can't go 30 yards without finding something you should be blowing up to advance the plot, enemies and vehicles and random objects to grapple hook onto, and playing with the crazy physics to make your own fun. Guns are the least fun thing here." Just Cause... 4, was it? Advertises doing a lot of crazy stuff in storms and wingsuit gliding and all sorts of action packed stuff... and the game is... "Wander through empty landscapes, never really see storms, you can't interact with them in interesting or meaningful ways, your tools are boring, and even grapple hooking isn't fun".
If your game doesn't match to what you're advertising, you will not have good sales. Your pacing can kill anything your marketing may have done.
This is one of the things I've always found to be weird about RPG advertising. These are invariably games about story, characters, and setting. Combat is a tertiary concern. Yet... most advertising for these games basically just shows nothing except combat. Turn based combat. The animations for the combat actions. The bland and boring stuff.
I pick an RPG to play based upon its premise and its main characters.
I picked up Final Fantasy X because the demo was so good. The music hit the right spots, there was enough mystery to not know what is going on, and the main character seems like a likeable, albeit very spoiled, kid. I wanted to know what was going on, what this place was, and what this kid was meant to accomplish in terms of the plot.
I picked up Mass Effect because the advertisement for it was basically, "You will have to make choices that affect the entire galaxy, and not all of those choices will be easy.". The game didn't really disappoint on that front either. I made a great many choices in the series... Everyone did. So many that the third game in the franchise was lambasted for the final choice "not really mattering at all". That's how effective the marketing was in telling the player was the gameplay was... and then in the gameplay delivering exactly what was promised by the advert.
For RPG's, I need some sort of set up. Who are the heroes? The villains? What's the challenge?
Heck, let's look at even MMO's and their advertising.
World of Warcraft's advertisements pretty much exclusively set up crazy storylines and action scenes and a "world defining event" for every expansion. Then, they don't really deliver all that well, or all that often. The gameplay doesn't reflect this and is instead "grind until you pass out from boredom" or "the story just got incredibly stupid and they retconned most of the story up to this point".
Then, you've got Final Fantasy XIV, which ONLY advertises the storyline in its trailers. Seriously, that's it. They give you some awesome music, they show off the "new content", they deliver "out of context" snippets of the story, with phrases ripped out of different chunks of the story, so that when you see them in the game, they are recontextualized. It's exciting, bombastic, and promises you a story that absolutely delivers. Meanwhile, their website just says, "Oh, we got crafting, housing, fashion, emotes, mini-games, racing, guilds, etcetera". Their game is primarily about the story... and the rest is stuff you stick around for after the story is done. Or, when you need a break from the story. The marketing sets the pacing of the game very well.
So, when you engage in marketing for you game, you need it to advertise exactly what your game is and what the pacing to be expected is.