I guess in the end I don't care who ripped off what of whom. If the game is good I don't care about its pedigree. Meanwhile let's pass out dozens of GOTY trophies to MW2 for all of its brilliant originality and innovation.
On the flip side, I don't want a reviewer saying any game of a beloved franchise is awesome just because we're not supposed to speak ill of that franchise.
Then you end up with the, "It's tremendously popular but perhaps long in the tooth, we should hate it and judge it far more harshly as a result," phenomena. This is very similar to the, "it has a huge following so we should make an anti-following," phenomena (see FFVII).
I'm not saying games need to be judged in a vacuum. Context matters, but feel like it played too large a roll int he ratings of both DI and GoW. DI wasn't super great, but it was solid and good. It was far better than the general it was given credit for by the growing machine of vitriol toward it.
Then there's GOWIII, which I'm still in the middle of, but it's good though not super mind-bendingly awesome. I think Yahtzee pointed out some good points about how silly it all is when all is said and done. It has flaws, many the same as DI. However, DI was cited for these flaws and told it sucked terribly because of them. GoW is said to be awesome in spite of them.
It's all because people got butt hurt about a little copypasta.
It's largely arbitrary in the end. DI is terrible because it's a rip off. 3D DGH, if the internet machine is behind, will be considered an homage.