The original Hack and Slash series was done several years ago. While a ton of things have changed with Unity, the series still works — well for the most part. Everything is still there, you just have to work around a few things now.
For instance, there is no guiText GameObject anymore, but you can still create one in Unity 5 by simply creating an Empty GameObject, and then just adding the guiText component. I would recommend learning the new GUI system that comes with Unity 4.6+, and integrating that in to your game. Another new tool is Mecanim. I would use this over the older system for almost all games. Sure, this adds to the learning curve, but both tools will carry over in to you future games better than the older systems.
As a result of these changes, I no longer support the series. I know there are a lot of people asking for a new version of the series, but understand the amount of time it would take to create that many videos again. I have learned so much since then, that I would do a lot of things differently anyway.
A lot of the newer series that I am currently working on have a ton of information that can be carried over from game to game. That is one of the reasons that I am doing them. Things like Raycasting, GUI, and collection coding are all good things to learn regardless of the game that you want to make.
The videos are still available on my YouTube channel for those that still want to follow along with it. It is broken up in to two playlists. and you can find them here:
Hope this helps,