Even if you don't care about your viewership, just recording a game of Hearthstone and then uploading a 40 minute video is, bluntly put, just super boring. If I was interested in a PvP game in general, and I look for videos of full matches, I rather watch people who know what they are doing and are experienced high level players instead of people who just started or casual players.
If I want to watch casual players, I want short videos - that's what everyone is telling you. Take whatever you recorded, pick out the funny and interesting parts, and put these together. Let me show you
videogamedunkey as an example - or
Vinesauce for the livestream end of the deal.
Longer videos are only good when you do LPs of a normal game, like Metal Gear Solid for example. And even then, most LPers keep their videos between 20 and 30 minutes. 10 minutes if it's a simpler game, like a jump and run.
A good rule of thumb is: Can you watch your finished video at full length without getting bored or jumping ahead?
Always watch everything again before you upload it, to see if everything works or if you want to make some adjustments. Another good idea is to wait a day or two after cutting stuff together before watching it again, so you had some distance and can look at it more refreshed.