It really feels like authentic Donkey Kong Country to me. Controls are very tight and responsive (even better than in NSMB Wii, which tends to feel a little like walking on ice and takes longer to gain momentum with Mario). Graphics are very nice, especially in the sillouette/sunset levels. Music is great for the most part, though doesn't quite measure up to the stuff from the older games.
There's just a great overall flow to the stages, and you can get around quickly if you're skilled enough, yet still can take some time on the trickier levels. There is a lot of variety throughout the games, in terms of the atmosphere and the obstacles. There is some degree of trial and error for some levels, particularly the minecart levels where you have to rely on fast reaction time to pull off. You're almost guarenteed to burn through lots of lives, but the good news is you can buy tons of them from Cranky.
My only gripe with the game besides the occassional trial and error obstacles is the need to constantly shake the remote for too many basic functions in the game. Also there are a lot of things to collect which can leave you wandering the level worrying about where they are rather than just enjoying the level, however, you don't need to collect puzzle pieces or kong letters to progress, so it doesn't affect the actual gameplay. I am just trying to collect all the kong letters on the first go round, since they tend to be easier to find, then once I beat the game, I will go back and try to seek out all the missing puzzle pieces.
The multiplayer is a lot of fun too, and I like that you can't hurt eachother/ knock eachother off cliffs. The game is tricky enough without that. I felt like in NSMB you were struggling against your allies more than your enemies, and they tended to get in the way, while in DKCR having a second player can really only help you.
But yeah, just a very fun old school style platformer. One of the best Wii games if not the best, better even than NSMB in many ways. Definitly better than DKC3, but doesn't quite reach the greatness of DCK1 and 2. Retro really did a great job doing their impression of Rare and its classic series.