Yes I have visited Warwick Castle for their Halloween event for the last 2 years and plan to return again this year. Personally I think it's a great event with something for everyone
For the last two years they have run an event called "The Haunted Castle" over the Halloween period. The opening times are extended to 9pm during this event and the whole castle is themed and lit up at night creating a great Halloween atmosphere. During this event the castle have also operated a few additional attractions which have included:
The Haunted Hollows - An outdoor family friendly themed walk through attraction with a few actors along the way. If your with kid's this is great too do during the day but if you're with older kid's or adults it's great fun to do after dark.
The Castle Dungeons (Paid attraction) - During this event they apparently step up the scare factor after dark. Although I hadn't noticed any changes to the normal day to day show.
Then there's the main attraction. It changes every year for example back in 2012 it was called "The Seance of Mary Black" but there is usually a walk through attraction that takes place inside the main castle that is aimed at adults and is usually pretty intense. In fact "The Seance of Mary Black" is still one of my favorite Halloween attractions of all time (and I visit all the main theme parks during the Halloween period).
And there are also many other Halloween themed activity's such as live shows, The fireball Trebuchet, Themed Actors, Record breaking attempts and Eagle displays.
Although the castle haven't officially released details of the 2014 event the attractions calender is showing 9pm close between 25/10/14 until 02/11/14 so this would indicate something is in the pipeline.
If you have any other questions about this event let me know