P. Julien It's very dark, much darker than Warriors, and the climax involves a pretty fatalistic view of the future. It's a haunting story, and I read it when I was 12 but I don't think you should let your sister read it for a little while.
Eloise I read this book at the age of 11, and loved it. It is not at all like Warriors, the theme is a little darker and deeper, but it’s an awesome book. There is actually probably less gore than Warriors, with the worst part probably being the Bran scene (which I won’t spoil) She might like it, as I did, but they are very different. To be honest, as someone who has read the whole Warriors series, The Sight is better.
Catherine It has similarities, but she might wanna wait to read it until she's, I don't know, 12? (The Named series, too, she ought to wait for. S'not quite appropriate for a 10 year old, I think.)
Ashley I love Warriors, but The Sight is not like it. That said, you can never know what someone will like. I'd recommend she try the The Named series. The first book is called Ratha's Creature, it's by Clare Bell.
Jane Being an avid lover of the Warriors series, I can safely say The Sight is nothing like Warriors. Personally, I didn't enjoyed The Sight at all, mostly for its terrible writing. Wolf behavior within the book is nothing like real life and sometimes you're just plain confused while reading it.