For some reason, I never posted in this topic.
Donkey Kong Country is the "one that got away" for me. I'm pretty sure I played DKC 2 once or twice since a friend of mine had it, but since we didn't get a Super NES until 1997 then I never really had the opportunity for games like this to have an impact during their time, having also gotten a Nintendo 64 in 1997. It also meant I didn't focus on getting SNES games until later, since the N64 took priority. Therefore, I never ended up with any of them until 2010, where I decided to buy the three SNES cartridges in the wake of the Donkey Kong Country Returns announcement.
Even though it was so late after they came out, I still had a lot of fun playing the games. Overall, the graphics don't hold up as well as some other SNES titles, but I actually feel the games still look okay and I didn't mind them. The music is the real highlight though, particularly in the second game which is one of the best soundtracks on SNES. The stage designs seem pretty varied in all of the games and I enjoyed most of the animal buddies. Some things like secrets can be questionable at times, but it wasn't a big deal... or at least not now that I can easily look things up. I do find it odd that Donkey Kong is not playable in 2 and 3.
As far as Returns goes, while I liked the game and was glad it had simultaneous co-op, I didn't feel it held up to the SNES classics which were still fresh in my mind having just played them. The game still has some pretty good level design most of the time, but it didn't feel as varied and it tends to rely too much on crumbling platforms. The music also sticks too close to the original soundtrack. Tropical Freeze was quite a bit better, while it still has the crumbly platform problem, the level designs are more varied and overall feel designed better. The soundtrack is also amazing, one of the best to come along in a good while. TF can without a doubt stand alongside the classics.
I'm not really sure where Donkey Kong 64 fits into all this. It's always tough for me to compare 3D games to 2D ones, however since DK 64 isn't one of my fave platformers on the N64 then I'd probably put it below the Country series. That isn't to say I didn't like the game, as I did enjoy its levels and its multiple characters with different abilities. But like most people, I do feel they went overboard with collecting. I think if they kept out bananas as character-specific collectibles then it'd be a lot better. Still, it didn't ruin the game for me, though I've never bothered with 100% completion (or whatever number is fully complete).
I also went on to get the Donkey Kong Land cartridges and I've played through those as well. They definitely suffer from the smaller screen, in particular the first game as falling below the screen border results in losing a life as if falling into a pit, even when there is actually ground below. Which is unfortunate, because the first Land game is actually pretty different from the SNES games and has its own themes and level designs. Land 2 and 3 stick a lot closer to their respective SNES game and have similar layouts and level concepts. Overall, they're decent for Game Boy but are no substitute for the SNES games.
I voted for "completed all" since I own them all and beat them all.