An interesting and surprisingly dark episode, in some ways, with very eerie undertones. The music in some parts is really creepy and near atonal (notably, in the holding cell right after the episode begins), Esoqq is terrifying in certain moments and overall extremely menacing, and there is just something...weird and off-kilter about the episode in general. And here's something: one just has to imagine if Star Trek was a slightly darker show, they end up being trapped just a little longer, and...well, it's entirely possible they might have actually shown, even if the worst details were off-screen, Esoqq attacking Kovar Tholl, killing him (or perhaps not), and then..."satisfying his hunger"...
Worse of all, then Picard would really have a serious bone to pick with the aliens, once he saw they had such little care about moral concepts that they were willing to allow a sentient being to kill and actually eat another sentient being in the presence of a third sentient being, all for the sake of "scientific research", and on top of that, Picard had to watch Kovar Tholl being eaten. I can only imagine what tone the episode would've had if it'd been like that. It certainly wouldn't have had the jolly, everyone smirks at the captain ending, unless it was really tonally inconsistent. It would have had one of those rare dark, sober, eerie endings which only a select few TNG episodes have, such as "The Mind's Eye", and "Schisms". Picard might have killed one of the aliens out of anger. Who knows? Just some food for thought - alternate endings are always interesting.
In reply to a couple of Jeyl's points, notably his two complaints about the episode:
1. About Picard's choice to (briefly, I might add) harmlessly imprison his alien captors to teach them a lesson: see what I said above: "all for the sake of scientific research". I may have misunderstood here, but do you believe the aliens should have just been allowed to get away scot free with abusing the rights of three life-forms? I don't understand this at all. It's better to be nice and gentle towards those who abducted you just for their research? What about the morality of telling them that it is wrong? Even if they didn't mean any harm, as they said - really not sure I believe them, to be honest - but for the sake of argument, let's assume that, even though their actions were deplorable, their intentions were genuinely not malicious or intentionally callous - they were simply curious. Even were this true, for Picard to simply let them walk away would mean that other life-forms would be at risk of being abducted and subjected to terrifying and potentially dangerous experiments - keep in mind that if Picard hadn't solved the puzzle soon enough, Kovar Tholl might have been eaten. Alive. Just because these aliens had no understanding of morality (what TV Tropes calls 'Blue and Orange Morality') doesn't mean for an instant that they should just be allowed to continue abducting helpless life-forms and abusing their rights. Otherwise, what was the point of the Federation even fighting the Borg? By this logic they should simply have folded, since the Borg "simply wished to improve quality of life". No...things don't work that way, and thank god for that. Roddenberry may have been flawed, but he always wanted to tell good moral lessons, and no commanding officer in his right mind wouldn't have stood up to the aliens by showing them - harmlessly, too - what captivity was like.
As for comparing this episode to Picard's treatment of the native aliens in "Who Watches The Watchers", I don't think there is any real connection other than that both alien species have different ethic concepts than the Federation. These aliens are nothing like the ones in Who Watches The Watchers. The situation is the opposite - they aren't a group of people who are primitive enough to believe Picard is a god because of the teleporter. Instead, they are so advanced that they call human linguistic communication "primitive" and have the power to create a facsimile of Picard. How is there any similarity? Of course Picard is going to be understanding and compassionate towards a group of fairly harmless primitive aliens whose only crime is being superstitious, and of course he isn't going to be so forgiving of a group of technologically superior beings who treated him and his crew in much the same way as Q has.
Finally, if the aliens really didn't know any better as they said, then explain why the moment they are imprisoned in the force field, they are terrified and say something like: "Our species cannot stand captivity, please release us!" - if they had such little understanding of how other species might feel about being kidnapped, how come they knew what it was like the moment it happened to them? It's more likely that they simply didn't care, being far more technologically advanced (this is established in the episode by dialogue), and had reached a level of technology where they clearly looked upon those of lower technological development as 'lower'. They may not have been evil or even malicious as such, but they were certainly callous, whether they meant to be or not. Picard absolutely did the right thing by teaching them a lesson. If he hadn't, he would have lost the respect of everyone and wouldn't have been the strictly morality-upholding Picard whom we know and love.
Also, a similar thing happened in Voyager when a race of aliens experimented on Janeway's crew. Her reaction was way more extreme than Picard's, and she was also absolutely right. Whether malicious and/or callous (as the Voyager aliens were, while these TNG ones were not so much), or not, arrogant species who abuse the rights of other life-forms need to be confronted strongly, not allowed to walk away.
2. About the facsimile of the female Bolian ensign turning out to be one of the aliens in disguise...I'm not really sure I understand your complaint here. If it was about the fact that she was the only female character in the holding room, I don't see how that's in any way a bad thing - first off, she turned out to be one of the aliens, not a woman at all, but (apparently) male, assuming the two aliens we saw were male and not hermaphrodites. Second, why would it have any bearing on the episode?
In any case, this episode is great. Very underrated IMO and highly interesting overall.