Galactus has had some merciless Heralds, but none more merciless than Stardust. While Galactus is happy to let you flee while he devours your planet, Stardust likes to make sure every last being from that planet dies and will chase down anyone trying to escape. True to her roots, Stardust in Snap is a new tech card that has a sweeping list of cards she yearns to combat.
Is Stardust too strong?

Before release, I've seen some worries that Stardust shuts down too many strategies, that it's a tech card that has too much application and is too generically strong. Let's look at which cards Stardust affects (shout-out to Ben Roller for help compiling this exhaustive list).

Among decks that Stardust can reliably shut down are Hela, Khonshu, Dormammu, Phoenix Force, and Doom 2099. These decks are heavily reliant on their key cards and are played late enough that Stardust can hit the board in time to stop them. Stardust also seems quite good against any Destroy deck that is built around X-23, Bucky, Wolverine, Nimrod, and Arnim Zola. There are ways destroy can be built to cope in a meta replete with Stardust, but several versions of the deck will struggle if Stardust has a high play rate.
A Surfer or hand buff deck that is relying on Brood, Makkari, Scarlet Spider, or Mr. Sinister for late power could be forced to retreat. Most of the time, Stardust won't be able to surprise your opponent, but playing down Stardust with priority on the turn your opponent attempts to use Blink or Lockjaw could be pretty devastating for Ramp decks. Notably, Mysterio, Agatha, and Ego should not be affected since those count as played, while Sersi and Polymorph change cards that have already been played.

While the list of cards Stardust affects is quite large, it's hard to get her out in time to affect some of these. There are an awful lot of decks that don't have any of these cards, and adding a dead 4/7 to your deck is especially bad value in a game with 12 precious card slots. Many decks can find ways to play around Stardust since, unlike cards like Shang Chi, Enchantress, and Luke Cage, she can't swoop in at the end and be an effective counter. Otherwise, they can just retreat for minimal cube loss.
Is Stardust too weak?

Unless you're sure she's going to have an impact in enough of your games, Stardust won't be worth it. That means she's meta-dependent. However, there are a few ways we can enhance her value. First, as a 4-Cost card we can get her out earlier with Zabu, which can help against some of the faster decks she would otherwise have trouble countering. Second, we can play her to mitigate the downsides of cards we play ourselves like Sentry, Gladiator, and Rhino. While decks and strategies have developed around turning these downsides into upside, they are indeed downsides that need additional cards to mitigate. Will being able to play a risk-free Gladiator or a lone 4/9 Sentry be enough to justify a deck slot?
Of course not. But it can give us a little added benefit in matchups that Stardust doesn't actively hurt our opponent. Stardust would be a more compelling card if there were more cards that positively synergize with her.
When to use Stardust
Most of the reason to play Stardust is to affect your opponent, so instead of building around this card, you should consider adding her to decks that specifically struggle against something she helps out with. Does your deck have a pretty good matchup against everything except destroy? Try Stardust. Having trouble with Gladiator/Fenris packages? Stardust can help with that. Unless something like Hela or Khonshu discard is the current meta tyrant, the main reason to play Stardust would be to shore up a bad matchup.
Scosco's Day One Stardust Decks
Zabu Tech Stardust
Out Power
Hands to yourself
Wiccan Star
Variants
Because Stardust is a more obscure character, we aren't getting anything from the Marvel Comics cover archives. Instead, there are several studio variants. It seems like Second Dinner is caught up on variants for new cards and a big part of that is the studios. Personally, I like the Creative House Pocket variant best.
Final Thoughts
Stardust is a meta-dependent tech card. It's better than some meta-dependent tech cards because it provides a healthy amount of points and is useful against a wide variety of strategies. However, it can't be played early, has low cube equity since it needs to be out in advance of what it's shutting down, and there are a variety of decks it will have no impact on.
So, should you get it? If you're the kind of player that likes to remain competitive and able to adapt to any meta game, you should be getting every tech card, regardless of how good they are on release, so how good Stardust is right now is largely irrelevant for you. Just get Stardust. However, Stardust is a card that you can happily live without, especially if you're a player that has your favorite few archetypes and/or decks and you conserve your resources to enhance those decks.
I don't think Stardust is too strong, as I've seen some suggest, but I do think it's a useful hate card. Her play rate will be high for the first week as people try out the card, but it will come down soon after. If it feels too strong, it is particularly easy to tone down in a future balance update, given its high power compared to most tech cards.