I finished it and thoroughly enjoyed it.
If you were expecting Discworld, you'll be very disappointed. Not only is it not like Terry's previous books, the whole pace of the book (and I'll include The Long Earth in this) is markedly slower. Whether this is due to Terry or Stephen Baxter, we'll probably never know and speculating about it doesn't achieve much. I haven't read any Stephen Baxter, so I have nothing to compare. But I do hear Terry's voice in there.
I would say that this is a satirical novel in serious sense. It's about humanities reaction to colonisation, immigration and the plundering of ecology. There are historical parallels such as start of the American War of Independence and the Role that Britain played in trying to keep control of its subjects by not doing very much except expecting loyalty and taxes.
There's abuse of sentient beings because they are considered sub human, and conflicts between humanity and sentient beings that fight back.
There's the almost unconscious sense that humans can take, take, take without giving back. The world close to the Datum seem to have been stripped of resources at an alarming rate. The use of the Twains, for example, is something that couldn't work here and now because there's just not enough helium left on planet Earth.
The resolution to the potential war was perfect to me. One of the things that the British eventually realised during the American War of Independence, was that they could never win. America was too big a country to send troops to subdue the locals. If the British attacked and fought the capital, the rebels would just set up a new capital in a different part of the country. It would never end. Likewise how can you subdue a people who just step away to another world. It's not a stalemate - as someone pointed out, the Long Earths make war obsolete.
Where I most hear Terry's voice is in the way that he knows humanity so well. He understands the human condition - something that hasn't really changed EVER. That has always been very clear to me in Discworld and his other books, and it's very clear in these ones.
So - if you were expecting funny and a traditional narrative, then you may be disappointed. But this series has a lot to say and is taking time to say it. These books are a parable for humanity and its future place on this planet and others.
“Men never commit evil so fully and joyfully as when they do it for religious convictions.” – Blaise Pascal