I agree that this ep is one of the best of the early TNG eps, clearly laying the groundwork for great things to come.
Having said that, and having just watched this episode recently for the first time in many years, there are some things about it that bug me.
Most of it has to do with Guinan. First, what's with that stupid cat-hissy-stance she takes with Q? She looks like she's about to shoot lightening bolts out of her fingers like Emperor Palpatine, or the Wicked Witch of the West. There is never any evidence that Guinan has any X-men super powers, so what was that for? It looked pretty stupid and I had to laugh.
More seriously, though, when you hear Guinan explaining the Borg and what they did to her people, I can't help but think, "Now you tell me!"
From what we know about Guinan, she has known Picard for a long long time, and thought of him as something beyond friendship, and obviously Picard felt the same way.
Even granting the Borg occupy a part of the galaxy that humans had not explored, it's just inconceivable to me that Guinan would not have told Picard what happened to her people.
I mean, this is who she is, a refugee from a destroyed and scattered race. Picard was not aware of this background? The Federation was not aware of this? I think my first action, if I were Picard, is to slap Guinan across her smug face for not sharing this bit of data with the Federation long ago.
Yet this revelation does not seem to bother Picard in the least.
Regarding the questionable decision to stay and investigate, in retrospect, this does seem foolish. But evidence would suggest Starfleet just has this curiosity instinct from way back. This is essentially the same thing Kirk does in The Corbomite Maneuver, so while perhaps questionable strategy, it makes sense "in universe".
The last thing that bugs me, is Pircards whining at the end and Q bailing them out, literally, a Deux ex Machina ending. I get it, that was the point of the episode and Q's actions, to show we are not ready.
But unfortunately, it made Picard seem inadequate, and impotent. If I had been a bridge crew person, and seen that seen, my reaction would have been to lose all respect for Picard as a leader. Maybe it would have been better for Picard to make that admission in the privacy of his ready room, rather than in front of all the bridge crew, whose very lives depend on his leadership?
Well, my opinion anyway.