Two replies to that. The first one is that I'm simply talking entertainment value here. Every now and then, it can be fun to watch our heroes go into action mode without any secondary thoughts or self-doubt whatsoever. Doesn't mean that I think that would be desirable in reality. When I'm in the mood for it, I enjoy watching Rambo-style movies where the bad guys get the shit kicked out of them. Doesn't mean that I think this would be a good solution in real-life antagonistic situations. At other times, I like to see deliberation, a Picard carefully deliberating how the prime directive should be invoked in this or that situation. But after watching several episodes filled with that stuff, it's just refreshing to me to see Kirk march into the thick of it, without being filled with doubt or being ashamed of carrying out his own ideals. Which brings me to the second point. In some ways, Kirk feels more honest than Picard does. Kirk is basically just a guy trying to bring his ideals into practice -- no hidden agenda as far as I can see. Picard however confesses that he believes that every individual/society (won't get into that debate here) has the right to determine his/its own worthy causes and ideals, and he also believes his morality to be superior for this reason . In other words, Picard is a hypocrite. I'm not sure there is a logical resolution for this paradox, but I would be willing to settle for Picard freely admitting that he does have a hypocritical attitude about this, and then move on keeping those same ideals, as he still believes that set of ideals to be the best, but in a more honest way this time. We never see this admission come from his lips, though. Which makes the TNG series kind of having an unpleasant inner tension for me that is never resolved, a tension that is not there in the original series. If anything, TNG shows me how unevolved humans still are in the 24th century. They have moved one step beyond the TOS century, yes, seeing for the first time that their way not necessarily is the best way for alle species. However, it is still a rational belief only, as a man like Picard does not seem to be comfortable with it at an emotional level. And it will still take centuries for humankind to develop to a degree that they can really incorporate that belief and accept other societies and species just for what they are. At least, that's the feeling I often get when watching TNG
The Borg were neither unstoppable nor something that could be dealt with only through the aid of a super powered being. We have seen the Borg as adversaries many times in TNG, FC, and Voyager. Only once were they aided by a super being (Q). He ended their encounter as abruptly as he had started it. But their later encounters demonstrated that our heroes were fully capable of devising original and innovative ways to deal with the Borg, from modifying their phasers to be effective to using the Borg's interdependency as a weakness to leveraging the effects of separating a Borg from the collective to even devising a "virus" to annihilate the collective (even if they ultimately decided not to use it). If anything, the recurring complaint about the Borg has been that they were defeated too easily; that their original status as a "super villain" was quickly watered down. No, I see no evidence of the Borg being an unstoppable foe that prevented good drama as a result.
TOS: Great chemistry between the Big Three and many unique and well told stories. TNG: Kept Star Trek in the public mind which helped us get more Trek. VOY: HUMOR, not taking itself too seriously, colorful and lively. And one of the most interesting character arcs in Trek, 7 of 9. DS9: Politics, development of whole cultures (Trill, Ferenginar, Bajor, Cardassia..) which had only been briefly seen before. Rich cast of secondary characters. ENT: Looks great, an arc that lasted a whole season, Jeffery Combs.