I had a few more thoughts I wasn't able to share this morning.
I think both the DKC trilogy and Returns have strong points and weak points. This is how I see it:
Graphics: Trilogy: Rare's use of pre-rendered graphics was spectacular in the mid-90s. Still holds up today.
Art direction: Returns. Every stage is a feast for the eyes, particularly the "shadow" stages.
Music & sound: Trilogy, by a mile. DKC2 boasts one of the best video game soundtracks ever made.
Level design: This is a wash, as far as I'm concerned. Amazing across the board.
Mechanics: Returns. The game is impossibly smooth. I even like the motion controls 
Replay value: Returns. The addition of time trials and mirror mode give it an edge.
Co-op: Returns, by a mile. A true cooperative experience.
Overall, I think Retro did an incredible job carrying the torch lit by Rare, just as it did an incredible job with its first borrowed franchise, Metroid. In both cases, Retro managed to match (in some cases, surpass) the great games that came before. And it also stayed true to the spirit of the source material, which is no easy task.
