FRLG are a lot of fun to me, and on reflection probably the only remakes in the series I find more enjoyable than the originals. What I like most about them, though, is definitely what they added to Kanto - the Sevii Islands.
I really like the Sevii Islands a lot. While I know many people wanted (and probably still do want) the Orange Islands to appear in a game I feel that the Seviis really did a good job of substituting for them. In fact the Seviis do double-duty in that they're substituting both for Johto AND the Orange Islands. And they did a really good job of it IMO. They were so unique and so full of secrets. And they manage to feel like a whole other region apart from Kanto and Johto. It's so unlikely we'll ever return to them which is sad; there's a mystique to the Sevii Islands that the other regions don't have. But it's nice that they still occasionally get referenced - I appreciated the little shoutout they got in USUM.
The decision to hold back the latter portion of the chain until the National Dex was a good one. Islands 4-7 feel slightly wilder and more untamed than islands 1-3; there's a sense that the further south you travel the deeper into the unknown you're going.
Of the seven main islands, Six Island is probably my favourite overall. It's absolutely stuffed with mysterious and characteristic locations: Dotted Hole, Ruin Valley, Pattern Bush, Outcast Island, Altering Cave. As a child playing FRLG for the first time I was obsessed with what the mystery behind Pattern Bush must be, even going as far as to Cut away every single grassy patch in there; it was so disappointing to learn that the secret is just "it looks a bit like a circuit board". Altering Cave, too, is delightfully weird if you don't know why it's there and completely fired up my young imagination (some people said that the cave layout looks like Mew... personally, I don't see it). Even the Green Path is a delightful little spot, with the two houses perched outside of the main town. It's almost certainly where I'd choose to live if I lived in the Sevii Islands (yes, I have my dream house locations picked out for each region, what of it). I also like the fun little easily-overlooked detail that a Rocket Grunt hangs out at Outcast Island before you defeat the Admins in the Warehouse on Five Island; it's easy to miss but cool nonetheless.
But the other islands have loads of stuff I appreciate. Two Island's Game Corner was always fun because I rarely had someone to play those games with (and still don't tbh - even though I have more than one GBA and wireless adaptors, two hands is not enough). Five Island's Lost Cave is spooky and surprisingly fun to figure out (it's somewhat similar in nature to Sinnoh's Turnback Cave) and I spent countless hours inside the Ice Cave looking for that elusive Sneasel. I was also far too proud of the fact that I worked out the trick to getting TM42 on Five Island without a guide; Pokemon games need more of that sort of stuff. Lastly, Trainer Tower was a fun change of pace from the Battle Towers of RS and Crystal. At that point in the series I was still appallingly bad at the mainstream battle facilities so having one I could reliably beat was appreciated. Too bad you can't use Thief to steal pinch berries from the trainers, though (yes, I tried and failed); had to wait until I got Colosseum to get my hands on them.
And of course there are the two secret islands. I have a great fondness for Birth Island; it was the first and only Gen III event I was able to attend (living in a small UK city will do that to you) but I managed to convince my parents to drop by the area where they were hosting the giveaway and download the ticket. I'd caught Deoxys by the time we got home 20 minutes later. I never got the MysticTicket, sadly, but I've still kept the save file with the AuroraTicket on it from all those years ago.
What intrigues me perhaps most of all about the Sevii Islands is that the game data hints at there being even more islands in the chain - location pointers for Islands 8, 9, 22, 23, and 24 all exist (why the massive gap? So bizarre)*. I've always liked to think that they could still exist - it's confirmed in-game that the chain being called "Sevii" because there are seven is a misconception. So maybe there are various smaller islands further away from the main archipelago; maybe we deliberately weren't shown the whole extent.
Lastly, I've always found it odd that people obsess over whether they're part of Kanto or not, but maybe that's because part of my family comes from Guernsey in the Channel Islands. For those not in the know, the UK has various island territories known as the "crown dependencies" (Guernsey is one of them, Jersey and the Isle of Man are others). They officially belong to the monarchy, yet are not part of the UK and are self-governing. I look at the Seviis the same way; they're part of the greater Kanto territory but self-administering and not beholden to the mainland.
So yeah. Big love to the Sevii Islands, perhaps the most unique main series game region of all.
*I've often wondered if the gap in numbers is intended to parallel how Japan's IRL route numbering system has large gaps, which the numbering of the routes in Poke-Japan mimics.
