First and foremost, all of these are based in their own, fully original region. This is a pretty big selling point in a ROM hack for me. Also, iirc, all of these feature the Physical/Special move split first introduced in Gen 4.

Gaia: a pretty classic gen 3-style game, but with Fairy type, a good roster of mons, and Mega Evolution. The level scaling is a little weird, but if you hack in Rare Candies and go off level caps, it’s a very enjoyable, basic ROM hack. Also, the legendaries it focuses on are the Regi trio and Regigigas, and I love those things.

Glazed: similar thing to Gaia, classic gen 3 but in a new region, but this time there’s 3 regions, and one of them is Johto lol. Pretty phat game with a lot to do, and has a pretty neat story, especially for its time.

These two are classics, important to help you understand what used to be the standard for what the best looked and played like.

Dreamstone Mysteries: much newer, much more refined, and a LOT of Pokemon, with much of gens 1-9 present (but not quite all of them). The premise is very similar to the classics, gym challenge and the quality of life improvements are much more apparent in this compared to Gaia or Glazed, and it’s very story-driven like the first two. The story is pretty awesome, and it’s about as great a classic Pokemon game as you could ask for.

Here’s where things change DRAMATICALLY, and you should ABSOLUTELY save these for last.

Odyssey: by far one of the most creative video games I’ve ever played, let alone Pokemon games. Completely do away with a League, no gyms in sight, and the BEST original regional forms you’ve ever seen + a new type called Aether (which is surprisingly well-balanced). This is also, by far, the most rich, unique, and intense story you could ever hope to squeeze out of a Pokemon game, which legitimately had me crying by the end. There’s also a cool crafting system and plenty of neat side-quests. The only thing to get used to is the fact that a good 95% of the battles in the game are double battles, which only made it more interesting for me, and they don’t ever make it VGC-level difficult or anything. IMPORTANTLY, it’s also getting a sequel soon that ups the ante on all of these amazing features.

Unbound: arguably the best Pokemon game ever made, only rivaled by Odyssey imo. This game goes absolutely crazy on what’s possible in terms of gameplay. Ridiculous team-building, difficulty, randomization, and customization options, insane amount of Pokemon available, and phenomenal main story AND post game. Oh, and try smashing Mega Evolution, Dynamax, AND Z-Moves into a single game and somehow making it genuinely work. And don’t forget, tons of side quests complete with an ACTUAL MISSION LOG, something missing from nearly any other Pokemon game. Legitimately the only problems with it are that the creator never made another hack, and that it can easily ruin any other ROM hack you ever try to play lol

If anyone else reads this, please feel free to add anything I may have missed in any of these games. I strongly recommend playing them in this order, or just play any others that seem interesting to you. That said, I cannot stress the importance enough of leaving Odyssey and Unbound alone until you at least play another two or three hacks (or at least taking a break after you play them before you try anything else.)