That's weird, because I haven't heard a single person (until you) complain that the action sequences in either movie were too long. Most criticism of FOTR focused on the linear travel-and-fight plot and the similarity between the action sequences, not that they lasted too long. Critics who didn't like the movie (Philadelphia Weekly, Hollywood Report Card, Richard Roeper, Juicy Cerebellum, etc.) complained about the overall length of the movie, but most of them pointed to the action sequences as highlights. Other major complaints I've heard were the over-repetition of musical themes in the score and the insertion of unnecessary sequences (e.g. the sappy romantic scene). Critics who liked the movie also pointed to the action sequences as a highlight - their minor quibbles lay in other aspects of the movie. The same goes for the people I've talked to about the movie - no single action sequence lasts over 10 minutes (including the multi-part "escape from Moria" sequence), so I don't think there's much to complain about.
This is also true of Spiderman. Few critics panned the movie, but those who did (Spliced Wire, Roger Ebert, Amazing Colossal, San Fran Chronicle, NY Observer, Apollo Movie Guide, etc.) never mentioned the length of the action sequences. They complained primarily about the script, either the plot structure or the schticky dialogue. Ebert, in fact, complained that the action sequences went by TOO fast. Critics who liked the movie had no complaints about the fight scene lengths, and I haven't heard this complaint from friends and acquaintances who have seen the movie. The action scenes in this movie don't last that long either (10-12 minutes at most) so there doesn't seem to be much to gripe about here either. There may be people who think the action scenes in these movies go on too long, but it was FAR from the largest complaint levied against either movie.
You're right about the proliferation of comic-book movies, but I think it's unfair to list League of Extraordinary Gentlemen in this category, because few people have even heard of the comic. I would list it with From Hell and Road To Perdition as a movie that came from a comic but almost no one who saw the movie knew it. For the record, though, League of Extraordinary Gentlemen is an amazing work and could be a great movie if it gets done the right way.