I often compare the series to redwall if you have read them. A lot of stuff about honour, loyalty, and blood, but more focused on the specific characters. Characters have a somewhat religious view about dead warriors, they believe that the dead watch over them and give them help in time of need. I have read every series so far except the last one which is still in progress (I promised myself I wouldn't start it until all the books were out). Although it has a very hectic plot development, after the point where I am, things seem predictive and repetitive. (Everyone knows shadowclan is going to stay depicted as evil, tigerstar is never going to officially die, and the medicine cat rule about kits is likely to be broken.) I personally enjoyed the series after having rejected it for a long period of time, and I look forward to any new series. Take it for what you will, enjoy reading it, but don't build your expectations too high from all the fan praise about it.
The cat warriors series summarized is like this (hopefully without too much of spoilers):
1st series: Discovering clan life, religion and politics. A super edition book explains that another clan once lived there named Skyclan which was forced away when Bluestar was a warrior.
2nd series: After separations are bound between the clans, alliances are required in order for them to survive. They learn to work together to come to safety to a new life in a safe land.
3rd series: Three cats together work to rise to power. One of them tries to uncover the past which may be the key of the origination of the clans, binding their stories together.
4rth series:
I haven't read.