The first was pretty cool, it had some cool features not done before, and for very early 2007, that was pretty f*cking impressive. Plus, co-op, can't go wrong. I used to love helping my mates out, them getting in a car and I would throw them through stunt jump rings before they had enough skill to get them. Or throwing other racers in the river while my friend would get first place, the definition of co-op.
But the second game, f*ck me, they ruined it. I didn't even buy it and it pissed me off. Played the demo and my god it was awful. Ruined the already copy and pasted map with zombies everywhere, took out the awesome agency vehicles, like the monster truck that could climb walls and jump, and the bad ass sports car that kicked vehicles up in the air. A lot of the map was destroyed and not climbable. Rooftop races didn't have a retry option and you would have to climb all the way back just to redo them.
f*cking god awful.
The trailer for the latest one looked too much of the same, and a lot like the tron aspects to Saint's Row these days.
Until we see some decent gameplay. I couldn't care in the slightest.