Like SpawnShooter mentions, the backtrack missions of DMC4 are bad because they add another layer of annoying artificial difficulty, rather than something interesting. The Dante missions more or less sucks because you don't get many chances to properly play around with his weapons during the most of 12, 13, 14, and 16. You're too busy being stuck with a stupid timer, a pointless warping puzzle, stupid octopi, and poison gas. 15 is almost literally replaying the level with different rooms linked together, leaving 17 as the only "unique" backtrack mission because you're now fighting on the ground instead of ceilings.
In that regard, DmC did much better by not including backtracking for the most part. Yes, the Virility Factory "foretracking" in the beginning could get a bit annoying after the first time around because you can't move any faster and the story exposition already served its purpose. But other than that, almost everything is new, and it's nice to see that for a change, especially when you consider that every DMC game before this had backtracking.
As for the original topic of this thread: yes and no. Some missions could and should have been longer. Mission 3 (where you get dash) and 15 (the trade) comes to mind here. I would say especially 15 because we could have seen even more of Mundus's power if the mission had a couple more "save car from world ending around it" sequences. Mission 18 could have also been a bit more than just one puzzle for the last non-boss mission of the game. I also would not have minded if mission 19 lets you fight Mundus alongside Vergil for longer than about 5 minutes before he gets taken in.
However, some missions would just be a test of endurance if they got any longer. Mission 17 (Furnace of Souls) is perhaps the most annoying mission in the game because the player can't zip past it even if he wants to. If it lasted any longer than it already does, I would have rage-quited on HoH and HaH. Mission 2, 5, 7, 11, and 16 are also plenty long enough as they are.
Overall, I'd say DmC hit a pretty good balance in terms of length. Some missions could have been longer, but most are about just right.