The latter IL books become even more Amber influenced. Not "rip off territory" by any means but noticing the relationship added to my enjoyment of them. if you've not actually read Amber before I recommend reading them before going on with the IL series.

I think you'll find, if you can be bothered with it, that Expanse Bk 2 is much more readable (though caveats about the plot of Bk 3 as I've mentioned before).