Not usually. It can bog down, in, IMX, the following circumstances:Frankly though, I don't entirely agree with the initial analysis of 4e. It isn't anywhere near as slow, IME, as it is being made out to be.
- Large parties - more than 4 or 5 players and it's stunning how rapidly things slow down, it's more than just linear. (By the same token, 2-player combats can be amazingly fast).
- Imbalanced parties - light on the strikers or none at all slows the race to 0 hps, not just because the party's dishing less damage, but because defenders and leaders keep the party chugging along longer. (Controllers can go either way.)
- Unfamiliar characters - when you run a campaign up from 1st on a fairly frequent basis, characters grow organically and players know them well (they even get to know eachother's abilities and synergies well). If you create characters at a higher level, or come back to a party after a long break, it slows everything down. You can also see this at Paragon, even in an otherwise smooth campaign, especially the first time you hit Paragon. There's a sudden bump in PC capabilities the first level or two of paragon. You get several new class abilities, a new feat (maybe a retrained-to-Paragon feat) and a new power all at 11th, another feat & power at 12th, and the availability of off-turn actions ratchets up in Paragon, too. (It's a speedbump, though, a couple levels in, things are back under control.)
- Inattentive Players; This is, IMHO, the big one. If players don't pay attention between their turns, every turn takes longer to play out, the wait between turns stretches, and more players become inattentive. It can be a death spiral. If you have a player who's in any way dissatisfied going into it, you have a weak link that can start that spiral quite easily, if any of the above start to do wrong, they can kick you down the spiral.
- Assumed player victory. If you don't mind TPKs, you can always dial up the threat until the party must win quickly, or die.
- Hating combat. If you can't stand it, the only good combat is a short combat.