This book had a very interesting premise. 
In regards to the writing it was solid. The book is told from the perspective of future Firmin and there are some points when the book become very immersed in the present, but whenever we come back to future Firmin it never feel jarring. However, there are lots of references to book in here randomly in passages - I understand this is Firmin's memoir and he is a literary rat, but it happens so much it gets a little annoying. Also, the lists in here (whenever they appear) are so long it is extremely excessive. 
This book is quite sad. Seeing Firmin's isolation

from his own kind and his inevitable failure to be apart of human society despite his desire to do so was very sad. 
Seeing his one sided relationships with humans was interesting and, despite knowing where they were going, it was quite sad to read.

I think that Firmin as a character is a little hard to connect to on account of

some of his more dodgy behaviours,

but he did feel consistent and me feeling sorry for him did make it easy to follow him along. 
While this book did make me feel sorry for him, I never felt really sad or heart warmed by any of this as it felt like outside of loneliness the emotional aspects of this book could have been a little more developed - however, this definitely does suffer due to him not being likeable.
<spoiler.Seeing the decay of the neighbourhood was cool.
It took me ages to realise that Norman and Shine were the same person. 

All in all, a very interesting premise - it did feel a little long at some points it was quite good and I believe it was worth the read. 

The cover was cool and the rat decals on the pages were fun.