The idea of a human bond with a telepathic animal (especially an alien one) isn't really that new...Dragonriders of Pern was a huge part of my own childhood...however, a lot of the ideas in this book are really quite novel and fun to think about.
Some of the points I found most interesting as concepts:
1) That the telepathic People/treecats and the verbally communicative humans can not actually communicate with one another, even when bonded. So very different are their communication methods that although they can reach an understanding, direct communication is not (in this book anyway) possible. Treecats just cannot seem to comprehend sound language no matter how they try, nor can humans ever directly discern completely coherent thought from them. This leads to a lot of interesting cultural differences and really influences the way the two deal with each other.
2) Primitive hunter/gatherer alien society with highly advanced humans. Not all that novel...and yet much of my experience in sci-fi does not have humans this far ahead of the aliens it encounters (in fact, usually it's the opposite dichotomy). But this does lead to a really interesting exploration of that society figuring out how to deal with the humans...avoid them and hide? Contact them?
3) Dealing with the pets vs. sentient species conflict with a species that is so different its intelligence is hard to guage and which really does seem to hit the human sense of "small, cute, and petlike" and what that means.
4) Interesting details about an imaginary human past...exploration of planets, contact with other sentient species (although it would have been nice to know more...we really only find out about one that did not go well), differences in biology, climate, gravity, etc.
5) Interesting and acknowledged details about where humanity has advanced (sub-molecular edged knives) and where it either hasn't or has keep the "old" ways as superior (modern style bullet rifles)
6) Examination of very complex human natures both good and bad.
However...all that said, the book also left a lot to be desired, mostly because it tended to have a very jarring flow with "snippets" of story. There is a decent lead up right until the time that Stephanie/Death Bane's Fang (main female human character) and Climbs Quickly/Lionheart bond...then the story immediately jumps ahead 3-4 years, completely skipping over pretty much all of them getting to know each other, Climb's Quickly's recovery from serious injury, humanity's initial reaction to treecats, Climbs Quickly's reaction to being introduced to much of humanity's culture/technology/etc for the first time, integration with the families (Climbs Quickly into Stephanie's and, to a lesser extent, Stephanie's into his when they visit him). Then it jumps around from there until it settles on a plot. There are long (somewhat dragging parts...well written enough but enough sidetracking from the story they're not really as interesting as they could be) segues into hanggliding, riflery, and so on. There are tantalizing little glimpses of other stories in the background (one example is when an entire treecat clan gets wiped out and another human/treecat pair is tragically involved) but you don't get to actually learn a whole lot about these. Then it finally settles on a plot involving a corrupt pet dealer that seems a bit...trite and rushed toward an ending.
There are also quite a few questions for me that just don't feel right...perhaps because of the jarring pace of the story. I wonder the following questions:
1) Why do so few treecat/human bonds form? When Climbs Quickly's clan first saw his bond, it was agreed more should attempt it...yet in 4-5 years, only 3 bonds form.
2) Did Kane/Kale (whatever the other boy's name was...I don't recall) actually form a bond with his own treecat or not? It seemed to hint that maybe and then didn't clarify at the end.
3) What were the other sentient species meetings like?
4) How did Stephanie initially prove to people that treecats were intelligent when so few except Lionheart every publically emerged? (It does seem to become generally accepted, even if the degree is not)
5) Although treecats learn some things from the humans (farming) they seem completely indifferent to much of their technology (they admire it perhaps, but don't really seem to want it or emulate it...with his "hands" which are dexterous enough to do things like make nets, Climbs Quickly seems able, but you never really see him using any of the human tools). Why is that?
6) The bond isn't really fully fleshed out. It's implied that it's like but not the same as a bond that forms between treecats when they find mates. Stephanie is clearly not impaired from finding a romantic interest, but those treecats that bond (all two of them) seem like they might end up single...does the bond with a human interfere with finding a mate?
7) Can the treecats bond with anyone or just "special" humans with a bit of telepathic ability already? The Dr. (can't recall his name) who bonds with Fisher (other treecat) has ability. It's not really clear that Stephanie does although it's heavily implied that she's somehow more empathic (toward treecats though not really other humans). Does this imply that maybe a really strongly telepathic human really could break through the communication barrier with a future bondmate?
Really...I loved the concept and many of the ideas but it's the pacing and general lack of information (that's tantalizingly hinted at) that makes me give this 3 stars...it leaves both wanting and dissatisfied. Long well examined details on weaponry and side tangents, big gaps on things that seem like they could be key story line. You could fit a whole book in between the initial fight with the Death's Bane/Hexapuma when their bond is really discovered and where the story picks up years later... And then the fact that the main villain doesn't feel real whereas other characters are so well examined. It's just kind of odd.
One additional note of disappointment - I tried hard to imagine how a treecat would look being six legged. I couldn't even fully decide how they would stand or walk around most of the time (I mean that I could think of multiple ways but couldn't pick the "right" one so I ended up assuming them to be essentially 4 limbed versions of Puss in Boots most of the time when reading). This could be easily solved by showing me cover art that didn't hide half the treecat.