Helldivers

Do you think it’s worth buying and do you thing the hype will last

it'll likely get stale after a month like most new games thesedays but if you want something like Helldivers playstyle and to play with friends you can try Earth Defense Force 5, its graphics arent as modern but has much more weapon variety and more fun.

The game is crossplatform right? but what does it mean that it's not crossprogression?

The hype will last not too long I think, I mean look at palworld