This is how I normally read books that I like. It usually takes me a while to get through the first half, but the second half often flies by like I'm on a roller coaster going downhill. The final chapters usually fly by at such high speeds that I am certain I miss details. The irony is that I've usually read portions of the end before I get to the halfway point (yes, I'm one of THOSE readers). Perhaps it's that bit of frontloading that makes my actual reading speed at that point cruise by so quickly.
Some books (Deathly Hallows for example) don't get the chance to go through this cycle as I crunch them in a single day (or night and early morning). However, those are rare occurrences where not only is it a story that I am desperate to read, but there are others chomping at the bit to read it themselves. At some point, I would like to write one of those myself.