Oh hey, great topic! I've been a fan of the Kirby games for a very long time--probably about 15 years, in fact! I won't say I've played EVERY game, but quite a few, and I'm familiar with the anime, Kirby of the Stars, as well. (In fact, I still remember first hearing about it on the Fox Box several years ago, and being all "OMG, there's a TV show about Kirby!")
Kirby games I've played:
Kirby's Avalanche - This was actually one of the first video games I ever played, and it was how I first became familiar with some of the characters--like Waddle Dee and Whispy Woods and such. I was never that good at it, and I only played it at daycare, but this was my introduction to the world of Kirby.
Kirby Super Star - The first Kirby game I actually owned. I have fond memories of playing it with my cousin when he came to visit; we actually completed it together. Back then I used to draw a lot of fan art for that game too, which got really difficult when trying to do Marx's wings, for instance. Marx is still my favourite villain in a Kirby game.
Kirby's Dreamland 2 - When I was little, I composed songs about the Kirby characters to the tune of some of the songs in this game. I have since lost the lyrics to them, unfortunately... This was a game I could never finish because it was too hard collecting all those Rainbow Drops. I finally did collect all of them just a year ago, but I still can't defeat Dark Matter.
Nightmare in Dreamland - I remember seeing the TV commercials for this game a lot. For the longest time, I didn't even know that it was a remake of an older game, Kirby's Adventure. The NES came before my time, anyway.
Kirby Air Ride - To this day, this is the only racing game I like besides Mario Kart. I just love playing through City Trial mode over and over again, because something different and funny always seems to happen each time. Especially when I end up on totally the wrong machine for whatever minigame we play at the end (i.e. I end up on a very heavy Rex Wheelie and the game ends up being Air Glider). Plus I LOVE the music in this game. Music-wise, it's my second-favourite Kirby game, just behind Super Star.
Kirby Super Star Ultra - At first I was skeptical about this game, as I already had the SNES original and I thought it was just a remake of it. But then I found out that it has several new sub-games, including one where I could play as Meta Knight (my favourite Kirby character), and I bought it in a heartbeat. I still love it to this day. Well, except for the fact that it's much harder to do multiplayer (two game cards are needed).
Kirby and the Amazing Mirror - A game I had completely overlooked back when it came out, and back then I was too occupied with Nightmare in Dreamland anyway. But one day, I finally decided to give it a try--in fact, I even did a blind Let's Play of it. I really like how the map is laid out in this game, and how it's all non-linear. Nowadays I like to fool around with the order in which I visit the areas, and defeat the bosses out of order and everything. Of course, as with Super Star Ultra, it's really hard to do multiplayer since multiple copies of the game are required.
Kirby 64: The Crystal Shards - To be honest, I wasn't really too excited about getting this game, but then my boyfriend got it for me, and I decided to play it anyway. It's kind of fun, especially with all the unique ability combos, but just not my favourite for some reason. And I'm still having trouble finding all those shards...
Kirby's Epic Yarn - Another one my boyfriend got for me. I really thought the developers did a good job of making this game really unique. I just love the design. I'm not too far into the game though, as I haven't had a lot of time to play it lately.
Favourite Copy Abilities
To be honest, I can't really decide on one overall. But I can think of a favourite in the context of certain games:
In Super Star/Ultra: Mirror and Ninja. I just love how Mirror Kirby looks, and the fact that Kirby can create mirror images of himself with it. With Ninja, I love how it features both close-range and long-range attacks. And I love the helpers for both abilities.
In Kirby's Adventure/Nightmare in Dreamland: UFO, hands down. I always rush to pick it up whenever I see a UFO enemy. I especially love the fact that it makes it much easier to fly, and to attack while doing so. And since I'm so used to Super Star's multi-technique abilities, I like how the UFO ability can attack with both a beam whip and various strengths of laser beams.
In Kirby 64: My favourite ability combos are the Fire Sword (Fire + Cutter) and the Animal Friend Statues (Stone + Cutter). Stone + Stone is fun too because it's just so awesome to walk over everything in the way, and I really like how Fire + Fire looks too.
But yeah, thanks for making this topic! I just love the Kirby universe, and there's just so much I can say about it.