I think the problem most people have had with Lets Kill Hitler, is that they were all expecting the episode to be about Hitler!
The title of the episode comes from what Mel (soon to be River Song) says to the Doctor as she hijacks the Tardis.
If you consider that Melody Pond was trained by the Silence to kill the Doctor, then it makes sense that she would be around Amy and Rory throughout their lives as they would eventually be with the Doctor.
When she commented about the last time she regenerated, she said it was into a toddler when she was in New York. If you consider the silence were probably guiding what happened to her and also the fact we haven't yet learned much about the eye patch lady it would be very easy for them to have settled her into the area where Amy and Rory lived making it simple for her to grow up along side them.
The regeneration in to River Song made perfect sense and it was a great way to explain the first time that "River" met the Doctor. Giving the Doctor all her regenerations for him to live, was also a good way to explain how she died in the library and did not regenerate. There is still more to learn yet, because the Doctor has not yet give her a sonic screwdriver of her own, but he has given her the book that she uses to record all her meetings with him. There is also the question of who the "good man" is that she kills. Personally, I think that it's Rory who she kills and not the Doctor, but that's just another idea I have had.
I suppose like a lot of things in life, its all to do with personal preference regarding the various story lines.
I know a lot of people seem to be intent on criticising this new series, a lot seem to criticise Matt Smith as well, but for me, I am loving it.