It's just not very funny - i LOVE Judd Apatow/Evan Goldberg and everyone in this movie. Superbad, forgetting sarah marshall, get him to the greek, pineapple express, and knocked up are all phenomenal movies in my opinion, but in my eyes they're funny because the characters are so hilarious and the situations are so normal. In This Is The End whilst the situations are entertaining and provide funny settings, the characters just aren't on the top of their game. The whole plot line with Jay and Seth was really stupid and unnecessary I found (although the side plot with Jonah and Jay was hilarious), and they never used characters to their full potential, especially the minor ones (Emma Watson, Aziz Ansari, Michael Cera etc.)
I really don't get why critics love this. I wish I could see it that way too as I was so excited for this movie.