How could we know how the franchise is if we only own a PS3 console? Well, I guess there's the option of owning an Xbox 360 at one time, and trading it in a long time ago.
In my case, I never owned a 360, had a PS3 all of last gen, but I have played a lot of the Halo multiplayer with my friends, because they owned 360s. I have been a long time TimeSplitters fan, and to be perfectly honest, the multiplayer in TimeSplitters can't even compete with Halo's multiplayer. Halo was just fun as heck back in the day. The only Halo games I have played are Halo Combat Evolved, Halo 2, and Halo 3, so I can't judge based on the entire series. With the PS3's massive collection of games, I wouldn't say the Halo games are the reason to buy an Xbox 360. Alan Wake is the reason to buy a 360.