#5 - Ratchet & Clank: A Crack in Time (Kudos to no-one for guessing this)
Although Insomniac Games are now my favourite developers of all time, mostly thanks to the Spyro trilogy, I thought they'd lost it when I played the original Ratchet & Clank. It just didn't have all the elements I associated with making their games great. Although Up your Arsenal corrected that many many years later, it was A Crack in Time that showed me the original Insomniac was still in there and capable of creating masterpieces.
For one, the game is absolutely stunning. A true pixar-style cartoony videogame. And yet it's not just that which makes it great - environments are truly beautiful; fantastically designed and with incredible draw distances. Those folks at Insomniac sure knew how to make the most out of the PS3.
Gameplay is everything you'd come to expect from Ratchet - blasting enemies apart with all manner of crazy weapons; solving environmental puzzles; zipping around in hover boots etc. The two additions to ACiT that made it better than everything else were the "planet" levels and the Clank puzzles. Both were fantastically designed and really expanded the scope of the game.
But what made ACiT best for me, though, was the story. Providing a resolution to Clank's storyline and even touching on Ratchet's origins in a very touching way; for a game like Ratchet targeted at a specific audience it told a surprisingly emotional tale. New characters like Orvus and Azimuth were incredibly well developed while Nefarious provides a formidable villain.
All in all, a fantastic way to conclude the Future trilogy (until the surprisingly appropriate Nexus 4 years later) and well deserving of a spot in my top 5.