Are they releasing all episodes at once or is it per week again ?
All at once.
I'm really interested in seeing how they try to improve this book since it's almost unanimously considered the weakest. You can already see some changed in the trailer that I really like.
Same here.
I went ahead and read several reviews because I was curious as to whether or not the critics would negatively allude to the weak aspects. No one did, really; the only real complaint I was leveraged (and this was from someone who ultimately agreed with all the rest of the critics that it's another great season) was that it's kind of too back-and-forth with its plots at times. Which is almost reassuring in its own weird way, since the reviewer mentioned the hops between Ilus and then Bobbie's and Avasarala's content being the issue at certain points but then that kinda just goes to show that we're getting a solid amount of their stuff as well which will help spread things out better IMO. That particular reviewer basically just said the high-watermark is still season 3 because everyone came together in that one rather than there being isolated incidents. So they'll get more of that later anyway!