My print copy of Cathulhu was all messed up (I was sent some book on Sudoku instead) but it finally got resolved and I have been reading through my print copy.
I have an admitted bias toward Chaosium RPGs, but Cathulhu is a really solid supplement. Some of the highlights include:
-A nice section on cat breeds with an emphasis on those available in the 1920's.
-Four pages of 'Tricks' which are mostly stat/skill bonuses some of which are based on breed ('Cat Burglar' adds to Sneak roll, 'Water Lover' adds to Swim roll, but only for Turkish Van cats).
-You have backgrounds of House cat, Farm cat, Stray/Feral, and Show cat (only for a Purebred of course) all give a bonus of some kind.
-A short but cool 'Bestiary of Feline Foes' section and which ones make for good eating is covered.
-An included adventure called, 'The Black Cat' which is NOT the adventure to play if your group expects a fun and silly night of gaming with cats as player characters.
I'll be stealing a fair amount (or unfair amount if you will) from Cathulhu though it certainly is playable using the standard CoC rules. BTW, cats do not lose Sanity, but rather lose Sentience and go feral in the end. A neat touch. You do have to think differently about how adventures will play out though, not like the cats can book a flight or steamer ship to Europe for example. Even a locked door can be a major obstacle.
That is also a positive though, as both GM and players learn to take different approaches to standard RPG situations. That sounds like a fun time to me.
If you want to try cat/pet gaming? You have a LOT of RPG options.