Rachel Najera I'd say give it a shot. These Broken Stars was slow paced and the majority of it was just Tarver and Lilac. Meanwhile, This Shattered World is fast paced, has a lot of action, and more characters with a different plot line. It's almost like starting a new series with a tiny bit of knowledge. If you thought the first book was just okay, you might like this one a little bit better.
Chelsea Depends on what you didn't like about TBS. TBS was also three stars for me due to overhyping and the majority of the book being made up of trekking. I then read TSW, and I kinda loved it. It had a lot more action and I liked the characters a lot more.
Julia I don't think it is worth buying, especially if you only thought the previous book was only three stars. I thought the first one was better, but thankfully there is a little more action in this one. I would borrow it from a friend or maybe the library. That's what I did because I felt the same way about These Broken Stars :)