The oddly large amount of time devoted to George's family per episode

Showtime kills it just as it starts getting back to the quality of the first few episodes.

The whole "appear different to the living" thing is an awesome conciet, but then we never see the alternate actors ever again (until the movie, anyhow)

The way George is given no time to grieve or adjust to her new status or, y'know, the loss of her entire support structure, and gets treated with an astounding lack of patience or tact from the other Reapers. Most of the various "fuck ups" she makes could have been avoided if Rube had just explained the reasoning behind the seemingly arbitrary rules he enforces.

Interminable flashback scenes with young George.

The fact that they apparently can't decide whether the reapers really do appear different to the living. The people they've reaped often recognize them. The actress playing Un-George/Millie is five years older than George and looks a bit older than that, but everyone still treats George like a teenager, and Un-Mason has grey hair, yet Mason at one point claims to have tried to get a modeling gig which required someone in his twenties. (Yes, Mason is not the sharpest tool in the shed, but the other reapers generally correct him when he's being stupid.)