Watched I-LAND as it was airing and this is a combination of some notes I wrote back then and my thoughts in retrospect now.

1. The setting for part 1 is basically a materialized barrier between those who are "in" and those who are "out". Like the judges discussed in the first episode, the resources and privileges you get at I-land create a conducive atmosphere for them to focus on training, while ground contestants have more limited time and resources. Although there isn't an immediate elimination risk, this incentivizes moving "up" to I-land. But it's a bit excessive to make a hugely expensive building in the middle of nowhere just to visualize that incentive to move up from ground to I-land, that came off as just an opulent and weird flex on BigHit's part. I also didn't like the extent to which they focused on this contrast and the "othering" factor, especially considering the method of determining who goes where (more on that later).
2. I liked that there were fewer contestants and no elimination in the first half. It allowed more room to focus on each contestant, gave the contestants more opportunity to appeal to the audience, and made sure one bad moment wouldn't ruin their journey. It wasn't executed quite that well and some contestants still ended up getting more focus anyway, but the scope was there.
3. The voting system in the first half was a dumpster fire. Starting from the start, in the first episode it was obvious that the sooner you perform the more of an advantage you'll have, and that's exactly what happened: majority of the seats were full before even half the candidates performed, and after that they started becoming more reserved with their votes and ended up eliminating some candidates who were better than some of the selected ones. Having the voting happening publicly where everyone (including the contestant being judged) can see who is voting yes or no also puts its own pressure and biases the decisions. Even following this, it was clear and even stated by some contestants that they were voting not just based on perceived skill/performance but also personal preferences. Early decisions and first impressions had long term impact as they essentially created a "class divide" - I-landers got comfortable with each other and were more likely to want their friends to stay, grounders also formed similar bonds, and despite the questionable system that created the divide, I-landers were perceived as collectively "better" than the grounders and that bled into their interactions when grounders moved up to I-land.
4. The change in system for part 2 did not improve much in terms of fairness. I guess they were going for unpredictability and if that's the case they were definitely succeeding but things did not make sense. Why alternate between producer scores and audience votes for different rounds when it would've been more comprehensive to combine both for each round and eliminate someone based on an overall score?
5. I did not like the way some people were villainized for dramatic effect when the conflicts could've been shown in a much more normal way. I know this is an mnet survival show so it is how it is, but I don't have to like that. Mistranslating what some contestants said, editing footage from one place to another for dramatic but untrue "reaction shots", and even editing contestants out of footage altogether to paint narratives, there's nothing they won't stoop to, and it sucks that the audience eats it up so easily. Even now, three years later, people keep hating some former contestants and painting victimhood narratives based on mnet's presentation of certain events. I'd wish mnet would have ethics but that would be in vain so I wish people would watch more critically.
6. While the performances were good, they were sorely underprioritized in favor of reality show-esque drama, be it for conflicts, emotional moments, wholesome fun, or guest appearances. It's not that I didn't like these aspects, they did help us get to know some contestants better, but I wish more of it had been relegated to additional behind the scenes content coz sometimes it did not feel like an audition show for building a kpop group. There's of course also the inherent bias in who got what kind of coverage (if any) and how that pretty much determined who makes it into the group more than the performances themselves.
7. Sometimes even the judges' feedback seemed outright scripted. Some criticism would seem like it came out of nowhere at a convenient moment when it was time to get rid of a contestant and the contestant in concern would always be someone who was already getting negligent or negative coverage. I wouldn't say it was outright rigged but it seemed clear that the production team already had an idea who they wanted and they had the power to make sure that those would be the contestants that fans would grow to root for as well. Any "unwanted" contestant could be rooted out by the judges, and the final group would be pretty much what they want it to be with maybe some contestants swapped out.

On the whole I would say it was kind of a mess, the premise was interesting and the contestants had potential, but it wasn't well structured, not executed well, and focused too much on stirring up dramatic moments and too little on the trauma it would create. I wouldn't say it was an enjoyable experience, nor do I think - in retrospect - it truly helped me know these contestants in terms of skills or personality.
On the positive side, the songs and performances were pretty good, and because of the low starting number of contestants, these new faces got more exposure and a better chance to make an impression than they would on your average survival show. Regardless of whether they made it into the final team, this was a good point of introduction into the industry.