Great game if a fan, average if not.
The gameplay is full of homages to the series, and every little thing that you remember about the series, chances are, it will find its way into this game. Laugh out loud bits are constantly thrown at you, much like in the series, until something will stick with you and you can't help but smile or chuckle or roar out loud. Unfortunately, this source material is the best the game has to offer.
The gameplay is simple and not very hard, with lots of health and ammo to keep you going through the levels as either Stewie or Brian. The weapons are different for each so gives you the chance to experiment, but other than going back to find the many collectables, is not really worth the trouble.
The various levels are all quite different, but again, once you figure out what you have to do and have found all the collectables, you might not want to bother repeating them to see their design differences.
There are challenge modes as well, but these too are simple, and the multiplayer for up to four people is strictly split screen, so make sure you have some more controllers if you want to play with your friends.
For me this had to be a buy as I am a huge fan of the tv series, but for casual fans, a rental would suffice as it will not take very long to complete and returning to Quahog may not be your travel destination as it was mine.