So. Let's Kill Hitler.
Definitely not my favourite episode, by far, and I can understand why people don't like it. That's perfectly fine.
But I feel the need to address two points that I've seen come up in arguments.
1. 'Mels' is a person of colour, who happens to have criminal tendencies, and this is viewed as racefail.
I'm not saying that people aren't allowed to have this opinion, although I see this as one of the weaker racefails of NuWho. Deana pointed out to me last night that it was interesting to see that Time Lord regeneration does, in fact, transcend skin colour (and quite possibly, gender). Given that we've only ever seen the Doctor as a Caucasian male, and other Time Lords (the Master, the Rani) have remained in their same gender/ethnic roles, it's something that has previously never been addressed, but has been plenty speculated by fans. And in this situation, I can't agree with the argument that it is racefail for a coloured Time Lord to regenerate into what we know as River Song, because River Song was already cast before this backstory was written. So if the racefail is a brilliant, confident, interesting female character worthy of the Doctor once again being cast by a non-coloured person, then the racefail happened way back in The Silence in the Library.
2. River Song is a fascinating character, who we find out is something of a Time Lord herself, and is more-or-less an equal to the Doctor. We can't have that, so she kisses away the rest of her regenerations, making her more 'normal'.
Uh, this argument is just... what. If River's story had been told differently, or had been written in a different order, I might agree with it. BUT.
We already know River can't regenerate because of The Forest of the Dead. If she had the ability, she would have regenerated then, and the Doctor wouldn't be all 'omgggg noooo Riverrrrr.' We have already established that she does not ever regenerate again, on top of the fact that Old Who has PLENTY established the giving/taking of regenerations, mostly between the Doctor and the Master. This is not anything new, and I'm not surprised by it at all. So, uh... I don't think it makes River less of an interesting, unique character, nor do I think it was pulled out of someone's ass. They were preserving continuity, which I applaud in my Doctor Who. In fact, I find it more angering that they decided to make her 'Time Lord-like' in the first place, because that implies that she wasn't an interesting enough character based on her personality.
In conclusion, I respect everyone's right to like or dislike this episode. I'm rather on the fence about it, myself. However, if you don't like it, I think there's plenty to be upset about more than this garbage.