I didn't notice any problem with Classic NES Series.
As for that game and the Double Pack, I imagine that it's because they don't have anything extra. Critics usually give less points when they don't add something.
And as for DXC, I imagine the score is 80 because it's not Rondo exactly, but a 2.5D remake. I'd like to think Rondo would get more than 90 at least.
MetroidVania is great, but every MetroidVania fan should play all the Classics, or they will be missing many great titles, being especially Rondo the best one to me.
Harmony of Dissonance is great in my opinion, but I know a lot of people that complain about the music and graphics.
In a proper console, graphics look very good. They look bad on emulators, I don't know why.
As for the music, it took me a LONG time to realize and understand what the composer was thinking, but when I got the progressive feeling, it became enjoyable to listen. I've been criticized a lot for liking that soundtrack, but I will always defend it because that's my opinion. Of course, I prefer the traditional CV music, but just as with LoD's music, I like it.
And I don't think difficulty should be so important when evaluating a game. I remember Rebirth being criticized for the difficulty, and it turned out very easy for me, so that I had to play it on hard and classic style, to enjoy it more. That way, the experience was fabulous.