This isn't a bad book by any means, but it didn't wow me. I think the reason is that sometimes it gets a little too close to what it's referencing.
Remember all those John Carter of Mars books and planetary romances like that? Yeah, so does the author, and he likes 'em a lot (Actually, so do I, though it's been a long time since I read one). This book takes place in an alternate timeline when someone or something terraformed Venus and Mars and then transported some life from earth to them. Thus you have a Burroughs-esque planetary romance with people, cave men, dinosaurs and exotic megafauna alongside a reasonably scientifically accurately depicted American expedition to Venus in 1988. There's also a rival Soviet base on the planet.
The adventure is modestly adventurous, but in the end it just felt too much like century-old stuff I'd read before, just made a bit more plausible.