Depends on which one you have....Sadlers Wells is present in so many lines there are many different traits present not all of which can be attributed to Sadlers Wells.
My lad who has Sadlers Wells as his grandsire is the sweetest thing in the stable. He did have a few issues with bringing in from the field but that was due to some previous dodgy handling. Now it's been sorted he's a total gent.
My horses grand sire is Sadlers Wells and he got a lovely temperament. He can get a little grumpy when im doing his girth up, but in general he is very dopey!