So about a week ago I found out about this game called Order of Avalon. It pretty much is an interactive RPG in SL (shockingly there are not many of these at all). I think it's definitely worth a check out at least for the scenery and lovely builds. First to start off there is a dress code of medival fantasy, but there are freeb outfits if you are worried that you may not have one.
The HUD is nearby and free, pretty sure you have to join the group to be able to participate but not entirely sure. There are many games to play and win various prizes. I highly suggest trying out at least past the first quest because you get some nice gifts. Here's a couple pics to help you get the idea of wearing things and puzzles and such.
I don't want to give away too much because it wouldn't be fun that way. Getting a couple friends together and exploring is pretty nice. Overall I know my eye is set on getting a certain amount of dragon kills (you need to complete the first quest to get to the dragon), after so many kills you can be able to get a dragon to ride. ^^
So overall all of this is free, fun, and definitely one of the more overlooked great experiences in SL. Goodluck. ^^v