Lol oh god, you're really asking a vanilla private server forum why does retail wow suck?
I predict the ensuing discussion will be unbiased and rational...
Edit: Ok, on a more serious note after watching the video this is what I think:
He is criticizing the overall design philosophy that WoW has and touches on a lot of points like the casualization of WoW, the implementation of queuing systems like LFR, LFD and others that inhibit interacting with others and essentially making you play the game solo, and the homogenization of classes.
Now, in my opinion, I truly believe if Blizzard hadn't made all of those changes to make the game more casual friendly, it wouldn't had experienced as much success and longevity as it has right now. The entertainment landscape of 2015 is vastly different and much more competitive than when WoW was released in 2004, I truly believe Blizzard realized that they needed to open up the content for a lot more players otherwise they game wouldn't last as long. So what Blizzard has right now in terms of content is tiered difficulty in almost every facet of of the game.
I personally think this system is better, that WoW is a better game because of it. But of course that's just my opinion.
I do agree with him on the fact that because of the implementation of the systems that I mentioned above it makes it a lot harder to socialize with other players, certainly I don't recognize anyone on my server apart from my friends and even if I'm not trying to be rose tinted about this issue, I remember when every server had it's own unique identity with its own sets of unique players and communities, that is sorely lacking right now in retail WoW.
Overall I think what Blizzard had done with WoW is that it is giving you more choices, do you want to play solo and not interact with anyone you're welcome to do so. Do you want to play casually only 1 or 2 hours every day, you can do so as well. Or you can play extremely hardcore with your guild and interact with the community if that's what you like.