Like many here, Super Star Ultra was my first Kirby game ,and man, did it leave one heck of an impression! The gameplay established in the original expands on that of all the then previous entries in the series, the gameplay itself is timeless, the variations of subgames keeps the game fresh and opens the door for new mechanics in future Kirby games as well as giving many of them clearer charactercization. My favorites are probably The Great Cave Offensive for it's exploration mechanics and Meta Knight's Revenge just for introducing the Meta Knights and being an epic mission in general.
Aside from the subgames, the Helper system also makes adventures more fun, the OST is fantastic, and it has some of the best bosses in the series.
Having gotten the game after Brawl (which Ultra released about a year after IIRC), I also noticed how many similarities the game shared with Brawl's Subspace Emissary, but it wasn't until I even found out that the game was a remake that I was realized which came first. The influence the original had on SSE is really evident, but I don't think it's a bad thing. Superstar and Ultra have incredible gameplay and along with Kirby's Adventure and Dreamland 3, set a standard for the series going forward. The game certainly got me into the Kirby series proper. I've gotten tons of Kirby games since playing this one, both old and new, and it's probably my favorite Nintendo series after the Legend of Zelda. The game's a ton of fun and has a lot of charm, but also some surprising depth as well, which itself soon became the standard for mainline Kirby games.
The remake went further than the original ,though, and expanded upon both the gameplay, various gamemodes, and even the characters. Dedede's character was expanded upon and his rivalry with Kirby and his full turn to an anti-hero was cemented for good in Revenge of the King, which also introduced Bandana Dee as a new major character, Meta Knights's goals and moveset were expanded upon in Meta Knightmare Ultra, which also brought back Nova and introduced freaking Galacta Knight, Helper to Hero gave the Helpers a chance to shine, and the True Arena gave Marx a truly nightmarish and memorable comeback with a difficult boss fight in Marx Soul, cementing his role as the entire game's final boss and continuing the tradition of Kirby games having nightmarish final bosses.
I have a lot of fond memories of this Kirby game and have it and the developers to thank for introducing me to the Kirby series, but I also think it's just a great game all around, and both versions of the game introduced a ton of new elements and established characterizations that stuck for future games. It's honestly an outstanding game, and I'd recommend it any day. Even to this day, it wouldn't be a stretch to say it's one of my top 10 favorite video games of all time.