Pokethulhu is a very humorous and low-prep game, great for one-shots. However, there are a few issues that stand in the way of using it for an extended campaign, mainly lack of rules for things such as catching new Pokethulhu, non-1v1 combat, and Devolution.
Also, all of the players need to be familiar with at least either Pokemon OR Lovecraftian monsters, though both is preferable and semi-required for the Owner (GM).
As it is, I would say the game is well worth the time spent reading the witty rulebook, and makes a great back-up for when you can't continue your usual game.
[5 of 5 Stars!]