I actually rather liked the series, so bummer to hear this. I originally picked up 1 & 2 budget because I didn't think it they would be great games. And indeed they had some serious issues, but I really liked the story behind it... a lot was kept or still is a mystery and I kind of liked that.
Still, it's not like it's I will really miss it either.
I can understand the last one sold quite badly. While normal games here cost 60 euro's and they initially sold Resistance for 70 euro's... when it was released among an onslaught of massive titles that all where 60 euro's.