You must have missed the old Crosby and Ovechkin threads
Anyway, at least on here, I think there are a lot of comments negative about McDavid are due to:
1. Him threatening the reputation of guys like Crosby and Lemieux (big reason why Penguins fans are outspoken)
2. Some over the top hyping of him by Oilers fans causes other fans to pile on him when he's not living up to that
3. Because the Oilers haven't had success with McDavid yet and people pile on the star players for not having success as a team (exactly what happened to Ovi before Ovi won his cup)
All of this is also partially due to jealousy of course, but I think those 3 would be the specific areas.