As everyone has already said, this suffers in comparison to Dragons Egg, as many sequels do. Without the world-building, it gets bogged down in technical details in places, and there were many paragraphs I didn't read because it became like wading through technical specs.
Some of the bigger issues I found: the Cheela at the end of Dragons Egg are "many thousands of years" beyond human learning at this point, and yet they still have very 20th century political and money issues. Perhaps their technical knowledge is better. As Star Trek taught us, technology moves faster than people think. Star Trek put communicators 400 years away, and we have better things than they devised just 50 years later. It's unavoidable, but to claim they were thousands of years ahead, I would have expected them to be in a realm indistinguishable from magic, transcending the physical universe. Better if he had said a couple of centuries, but that's quibbling.
I also found the Cheela changing their names at major events hard to follow, especially as they are short lived compared to humans and change anyway, but actually we don't get too much character so it wasn't nearly as bad as the technical parts.
Although you could feel the 1950s sensibilities of the author, it was lovely to see him trying for better. A few times, I expected the joke to end up sexist and he surprised me by going the other way. James Hogan has become difficult to read because women are always beautiful and worship their bosses, and the men smoke in literally every scene. Forward did much better here, despite the fact that it is a period piece, as all things will become.
I read Dragons Egg in the 1990s, just out of university and loved it. I read it again in my late 40s and it's becoming old fashioned, but it's a great idea and he's told a story well. There's a few bits he had to hand-wave, because it's fiction, but it's a great book. 5* for Dragons Egg, but 3* for Starquake.