Thank you very much for taking time to play and write this lengthy feedback, it's very much appreciated!
The "disappear" bug you've seen has been only reported once a few months ago by a partner and for them the only solution was to create an OpenGL build rather than DirectX. We couldn't reproduce it in our end in any case so it's something mistery for us as well. We'll keep an eye on that but the good point is that it didn't affect your play in your subsequent try(es).
This is an Alpha build with a few missing items and known bugs. Some missing features are Keyboard support and ability to redefine GamePad buttons which will be included in the final game. Defining the GamePad type is also in the todo list and than we'll update the gamepad icons in the game according to that. Escape key behavior is something I had done for myself to quickly quit the game and forgot there, so that'll change in the final game as well.
One interesting request of yours is to be able to tumble even while you are blocking. At the moment, as you've probably noticed, you only affect your blocking direction which is a purely visual effect and nothing to do with the ability of blocking (even somebody attacking from your back will be auto blocked if you are pressing the block button at that time).Overhauling/reviewing the combo system for a more easy approach is in the todo list and at that point I'll also review this to see how it affects the balance of the gameplay. If it feels right, I'll add it and it will be your contribution to the game .
Finally, I'm glad to hear that you liked it and once more thank you very much for taking time and writing back your feedback!