After the fourth book, which left me a little bit less satisfied than the other novels, I took some time of reading the series. While not completely forgotten, I didn't think a lot of the series and since were library books, it took another three years for me to finally start reading The Last Olympian. And I'm really glad I did read it.
It took me a day. That says enough. I switched to the English books for this one, and although I nowadays prefer reading English I got the impression that the Dutch translation was quite good this time, as I had no trouble to adjust to the English writing, and it all had the same feelings surrounding the writing. The humour also stayed the same, as far as I remember.
It took me a little time get back into the story. Obviously, after three years, not every detail was completely fresh in my memory (the 500+ books I read in that time probably didn't help either), but this wasn't a problem as it all came back really fast after I started reading. I immediately remembered the mythology that made me really like the series to begin with. In this volume I appreciated the inclusion of the so-called minor Gods, like for example Morpheus (after which morphine is called). I've always had a soft spot for them and never understood why they didn't deserve a bigger place. I can't blame them for not stepping up to save the Olympians.
This is the endgame the last books have been building up to. Is the ending a surprise? Not really. Does this matter? Not really.
I'd recommend the whole series.
The Last Olympian is the final book in the Percy Jackson and the Olympians series, the previous books are The Lightning Thief, The Sea of Monsters, The Titan's Curse and The Battle of the Labyrinth.