Let me put on my "back in my World of Warcraft days" hat for a moment. For the longest time, my playtime in WoW was dominated by being in a 25-man raiding guild and I loved it... until Blizzard announced that they were equalising the rewards for 10- and 25-man raids, and people predicted the end of large group raiding as we knew it - including myself. My own 25-man guild was forced to downsize only a few months after the initial announcement, and many others followed. While the format hasn't died out completely (as far as I'm aware anyway), there was definitely a big drop in player participation. The fact that 10s and 25s had to share the same lockout from Cataclysm onwards supposedly didn't help either, though it's hard to tell exactly how much of an effect that change in particular had on the exodus from the 25-man raiding format.
Why all this WoW talk, you ask? I mention it because seeing the game change to equal loot and a single lockout for both raid sizes made me quite unhappy at the time, seeing how my entire play revolved around the old system and Blizzard basically broke it. However, The Old Republic copied all these changes and made them part of its operations system from launch... and somehow, dealing with things being that way from the start and accepting it as a standard part of the game, I haven't minded nearly as much.
For the first ten months or so of me playing SWTOR, 16-mans might as well not have existed. I was in a small social guild that only did 8-man and that was that. I had no interest in 16s, nor any particular desire to learn more about them. However, when I joined Twin Suns and got a taste of the bigger format for the first time, I loved it. It was the closest thing to 25-man raiding I'd experienced in a long time, and we were doing it regardless of the rewards. We weren't exactly a 16-man guild, but we were large enough to do the bigger format occasionally, and it was fun.
However, not everyone in the guild shares my view on the subject. For quite a while now, running 16-mans has been a bit of a contentious subject in fact, as there are basically two factions in the guild: those who enjoy it and those who strongly dislike it. We currently have two 8-man progression groups and if we put the two of them together we could easily tackle some challenges on the harder difficulties, but once you subtract all the people who don't want to come to 16-mans, you suddenly come up way short of a proper team.
One of our two guild leaders, who is one of the main advocates of doing 16-man content, has recently put 16-man TfB on the calendar for Mondays, and basically takes whoever is willing to come. Most weeks we end up with a core of about 10-12 guildies who are happy to tag along plus a couple of friends from other guilds filling the gaps. Oh, and did I mention that due to the shared lockouts pretty much everyone is on an alt (since we need our mains for the 8-man progression)? If you think that this slightly hodgepodge arrangement makes serious progression on 16-man harder, you'd be right... but it's not impossible.
It's definitely more challenging to herd sixteen cats than eight, but it's somewhat balanced out by the fact that 16-man is designed to leave more leeway for mistakes. This wasn't actually true in some of the earlier operations, but by now it seems to me that the devs have managed to find a pretty sweet spot in regards to balancing. The content is still appropriately challenging, but you can take along a couple of pugs or slightly underperforming players and still make it.
From my perspective I've been finding the change in healing requirements between the different sizes the most interesting. In some ways, 16-man healing is less engaging because there is just so much cross-healing, it's hard to feel personally responsible for anything. However, at other times a boss will suddenly throw you a curveball by unexpectedly ramping up the damage of a certain ability that hardly hurts in 8-man.
This was the case with Operator IX on hardmode for example, where the AoE damage during phase two whenever his shield is up suddenly seems insane on 16-man. We eventually switched to doing the fight with five healers just because we kept losing people in that phase. This week we finally downed him, after weeks of wiping over and over and only making fairly slow progress. Even though this is something that we did on 8-man months ago, it still felt very rewarding in its own way.
I do wonder how many people actually care about 16-man operations though. I bet there are a lot of players, even among those who do raid, who are the same as me while I was still in my small social guild and don't even give a thought to the bigger format. And my own guild culture shows that even among those who could easily participate in 16-man content, there is a significant number who simply don't like the larger groups. It would be interesting to see Bioware's metrics for this, in a game where larger raid size never had the same status as it did in WoW.