Some background: I used to read mainstream superhero comics, mostly in the Marvel superhero setting, mostly the "mutant" X-books. And, frankly, most of them were atrocious.
I've also had a few forays into the DC supers universe, but mostly via the Vertigo (eg, Sandman) titles. These were not nearly as bad, but they also were not "superhero" books in the sense that I would hazard James is using the word.
Perhaps it would be helpful to define what a SuperHero Comic book is. Lemme take a whack at it:
1) At least one of the main characters has superhuman powers (flight, throwing lightning bolts, mind-reading, whatever).
2) At least one of the main characters either wears a cool-looking costume, or happens to look cool naturally .
3) The superhuman powers are employed to combat the characters' enemies. (criminals, aliens, zombies, whatever).
4) Illustrations are integral to the story-telling medium. (Ie, the Wild Card novels are not superhero comics, nor would putting the occasional drawing into them make them comics.)
These criteria are the ones that, I think, pretty much everyone will agree on. Of course, by those criteria, "Sandman" is arguably a superhero book--though not really, because the book isn't really about using powers to engage in conflict.
However, "Watchmen" indisputably fits these criteria, as does "The Crow", "V for Vendetta", Matt Wagner's "Grendel" and his "Mage". These are, incidentally, all solidly-written and well-illustrated works, and I highly recommend them. If you haven't read the original four issues of "The Crow", you might find them particularly noteworthy -- they're black and white, but some of the pages have almost a water-color look to them. Lovely stuff. Much better than the movie. But I digress.
This much said, I think these are all books that James would say -- with some justice -- are not superhero comics. So what else makes a superhero comic?
5) A superhero comic does not have a planned ending. Superhero comics get cancelled, yes. And sometimes, authors wrap up the story neatly with the cancellation. But this is not because it was planned that way: the death of the book is due to waning popularity, not authorial intent. By intent, the thing is meant to go on forever, like the X-Men and Superman titles.
6) Superhero comics have continuity. It may not be very well-maintained continuity (I distinctly remember one of too many low points in the Excaliber title: when Kitty Pryde turned 15. For the second time) but it's there. What happened in previous books is meant to affect subsequent books. Unlike the typical primetime TV series, the characters do not remain frozen and unchanging, with each episode completely self-contained and having no impact on the next. Superhero comics are usually more like soap operas in terms of the connection between stories -- and, sadly, in terms of the overall cohesiveness of the tale.
7) Superhero comics take place in a shared setting with other authors who write other superhero comics. This one is a little more controversial, perhaps, but I think it's integral to understanding the whole phenomenon. What happens in a "Superman" issue has the potential to affect what happens in a "Batman" or a "Swamp Thing" or a "Wonder Woman" issue. If the author of "X-Men" blows up Philadelphia, then Philadelphia is gone from every other Marvel superhero title, too.
It's these last three criteria that eliminate all those books I named above -- even the ones that make it past #5 and #6 don't fit into #7. Those authors were all flying solo for their works.
Criteria 5-7 are the ones by which superhero comics, as a genre, have lived and died. It's the continuity that keeps fans coming back. It's the familiarity of the characters -- old friends that they grew up with, that will be there, month after month, as long as the title remains economically viable. And it's the richness of the universe -- all that background material! All that detail! All those different voices that have contributed! -- that make the stories seem so real, despite the implausibilities.
But these are also the very things that make superhero comics terrible. The two big universes, Marvel and DC, are drowning in details, most of which are, frankly, stupid. Mistakes made by some hack who wrote three issues of a book before he was canned are kept alive for all eternity. The poorly-thought-out powers of one author's prized creation become the albatross of every other writer in the setting.
And the stories can never be finished. No matter how much the character has been through, no matter how sick the author is of writing about him, no matter if he's already been married twice, had kids, saved the Earth eight times, saved the Universe five times, and most recently fought off the imminent collapse of Reality Itself and All the Multiverses from the screaming hordes of garguatian Space Locusts -- no, we still need to have another issue about him next month. (But hey, your readership is way up! Think you can come up with something more spectacular for the next story?)
So: is there hope for a superhero book that fits all of these criteria? I really don't know. I think #5 is the hardest part. It's very draining on an author to never be able to bring the project to a close, to wrap it up with a ribbon and say "ta-da! I'm done!" And it's hard on the characters, too, who begin to seem more and more absurd as they go through adventure after adventure, each one more spectacular and implausible than the last. ("You did all that?!" "Well, yeah, that was preety much everything from last year. Did you want to hear about the nine before that?")
I haven't read DC or Marvel comics in 8+ years, so I don't know if they're terrible nowadays or not. But with such a long burden of bad continuity saddled on them, it's difficult for them to rise above it and become good. But I expect there are exceptions.
There are some good superhero comics being written today, outside of DC/Marvel, that fit several of my 6 criteria. I recently read "Confession", in Kurt Busiek's "Astro City" setting. I believe that's a setting with continuity, though I don't think it's a shared setting, and the story arcs don't go on without end.
CrossGen is a fairly new comic-book company that appears to be aiming for criteria 1-7. I haven't yet seen the sort of cross-comic-book continuity that characterizes a shared setting, but the possibility for it is clearly there. The best I've read of their titles is "Negation". You can read some of their books for free on the web, which is kind of cool, but I find the interface a bit clunky. (You need Flash and ActiveX turned on, and unless you've got a 30" monitor or really good eyes, you'll need to mouseover or scroll through the word ballons one at a time to read them). CrossGen isn't strictly aiming for the "superhero" genre, however--they've got a "superhero" framework that seems to run throughout the various titles, but each individual series has another genre -- detective, medieval, fantasy, sf, etc., that it also fits into. "Negation" is a space opera/superhero crossbreed story. "Ruse" is a Sherlockian/superhero cross, and also not bad. But, whatever you do, don't read "Mystic". Just ... don't. CrossGen is an interesting experiment: it has the most promise of the "shared setting" comics companies that I've seen. But, that much said, I'm not as enthusiastic about their works, even "Negation", as I am about the other comics I've recommended in here.
But I am going to make one wholehearted, enthusiastic, and unreserved recommendation for a superhero comic in every sense of the word: Alan Moore's run of "Swamp Thing". This isn't a current series -- Alan Moore wrote Swamp Thing for three years or so back in, I don't know, the 80s. But it's still available in graphic novel format today (you can find the first installment here) and it's got it all: superheroes, continuity, combat, shared setting (Alan Moore has an amazing talent for taking other people's old, tired, lame-brained ideas and making them into something REALLY COOL), continuing characters, etc. Moreover, you don't need to read any earlier comics to follow what's going on in this series. As with "Sandman" and G.K. Chesterton, you might enjoy the "Swamp Thing" story more if you've read other DC titles, but you won't be lost without that background.
And ... I think that's all I have to say about that. Maybe this was a little longer than strictly necessary. :)