I'm going to say this right now. I haven't really watched a lot of this person's videos. So I would suggest you take this review with a grain of salt.
However, after I watched the first few episodes of his Emerald Let's Play, I became incredibly bored. I know that people (even the main article itself) praise him for always having something to say during even the most boring parts of the games he plays, but personally, the problem is that he constantly talks about the Pokemon metagame. I know that the topic may interest other people, but in my opinion, the metagame is something I don't necessarily care about.
And that's one of my biggest complaints about Slowflake, as well as what I believe is a general flaw. If someone only talks about one thing, people will become uninterested, especially when they don't care about the one thing they always talk about. I kind of wish he would talk about what was actually happening in the game rather than something that was barely related. Take Chuggaaconroy for example. He menages to recall anecdotes of his life as well as show reactions to the game itself, which is what I think makes him a very good LP-er. Add some of my, admittedly petty, pet peeves in (not nicknaming Pokemon, using Legendaries on the main team) and I lost interest in Slowflake rather quickly.
I don't know if Slowflake has improved over time. Maybe he has, maybe he hasn't. Unfortunately, he already made his first impression, and it wasn't a particularly interesting one.