The first Pewdiepie video I watched made me think, "how can anyone enjoy this?" The way I see things though, if I don't enjoy his videos it just means it isn't made for me, so I have no reason to hate on something that was geared for someone else. I think the first thing is to pick a demographic that you want to appeal to. IMO a teenage audience would be easiest because unfortunately I don't think many older people on youtube will subscribe to someone that's younger. For example, I think it's easier for linus to have a mass appeal than someone your age trying to do the exact same videos that he does.
As for what I look for:
relatability
quality
original content
be yourself
Things I don't like:
Ali-A/tmartn
obnoxious people (an example IN MY OPINION would be phillip defranco)
content copiers/re-uploaders
people who don't seem interested in what they're saying/doing
people who try way to hard to be something they aren't
starting videos with "SUBSCRIBE AND LIKE MY VIDEO" before it starts
I might edit as I think of more things, but generally teenagers are the easiest to appeal to, and it's always a good start.