In my mind, there are generally 3 ways to approach the good ol' first contact story:
1. Make it about the mystery, embrace the unknown, and keep the aliens under wraps and off the page. Tease us, but save the aliens for the big reveal (or don't show them at all).
2. Go all-out with the monster angle, use the readers' fears against them, and exploit the very nature of being alien. Tease the readers for a bit, then allow the monsters to explode from the page.
3. Make it about the integration of two different worlds, and explore the society angle. Drop the aliens on the reader right away, integrate them into the world, and explore what happens.
The problem with Heaven's Shadow is that, for a long time, it doesn't seem to know which approach it wants to take, resulting in a novel that samples them all, and providing us with a story where the whole doesn't live up to sum of its parts. The best parts of the story are in the first third, where the astronauts begin to realize that their rogue asteroid isn't wholly natural, and may in fact be home to the remnants of an alien civilization.
The struggle between the duty of exploration, the joy of discovery, and the fear of the unknown is handled very well, with the astronauts coming across as both human and professional. The second third has its moments, particularly in the first reveal of the sentinels and the remnants, but the story just can't sustain matters. As for the final third, it just becomes a jumbled mess that fumbles nearly all of the many of the balls it was juggling. The sheer lack of professionalism at NASA is ludicrous, the almost complete lack-of-reaction to the impact of alien probes is ridiculous, and the blink-and-you'll-miss-it Rapture would be comical, if it wasn't so strained and out-of-place.
It also needs to be said that the portrayal of women in this book is atrocious, and that's not an issue I generally take notice of. They're all weepy, emotional, fragile wrecks who are defined as much by their relationships as their reactions . . . and who, it is suggested, are possibly not fit to be astronauts in the first place. It didn't really strike me until near the end, but if it wasn't for their crying, bleeding, and overreacting, first contact could have gone much better. At almost every stage, it's the mistake or overreaction of one of the women astronauts that acts as a catalyst for disaster. Once you realize it, it makes for a very uncomfortable read.
All-in-all, a novel that begins well, stumbles in trying to find a direction, and ultimately falls face-first in choosing the wrong direction. There's a sequel to come, but no interest here.