Not to derail the thread - but I've never played 4e, only watched my friends playa couple sessions before they went to PF. The one common comment made about 4e as people went up on level was the extremely long combat times due to the various daily powers and tactical nature of the fights with numerous comments saying 6 hours for some fights. When you mention streamline in 4e, what are you referring to and you or others can PM if you'd like and I'd appreciate it either way.
First off, I want to say that I don't see anything wrong with a 6-hour long combat
as long as the combat is interesting during all this time. That is the major difference I see between 3e and 4e (the two D&D editions I played the most).
In 3e many fights would finish in a round or two at mid/high levels, but the combat was really, REALLY long. Because the characters had a bunch of options that could potentially halt the action for math reasons. Eg, you could level drain, exhaust, shivering touch, enfeeble, etc... a monster and that would require the DM to recalculate almost everything in the monster stats. Or they could summon a monster that would break the action economy because now that player could act 2+ times per turn. Or the ranger had a pair of Wounding scimitars that every two hits we had to recalculate the HP the monster because HD was not linked in any logical way with the monster's CR. And I didn't even started talking about how you could have six buff spells, each giving a different bonus type to the same thing, and you had to verify any odd-case casting if that would stack with what was already used or not.
In short, 3e combat was "short", but was tedious and filled with minutiae. You had 20 minutes combats, but that was 5 minutes for each character mostly doing math and not "making decisions" (aka, playing the game).
In 4e, there is very few things (outside dailies) that affect the game for more than one round. The game also assumes you are throwing X monsters against X PCs (instead of the old CR rule that assume a single monsters against a 4-person party, and then good luck if your group had a different size), and also most (non-elite/solo) monsters don't have special attacks beyond a single encounter (or recharge) attack and their racials/basics. This
diminishes complexity at the same time it adds depth. So, while on average a 4e combat would last 60-90 minutes, it could last from 6 to 10 rounds, but every round the player would make an important tactical decision to finish the combat. A single individual turn hardly would take more than a minute or two (unless your group REALLY like to talk through every option, but any DM can easily set a time limit for discussion and thinking), and you knew your turn would come back before 10 minutes had passed.
In short, 4e combat was "long", but it actually required you to bring your best tactics to each round, and requires good group coordination to pull off the really impressive tricks. The combat took a long time, but it always had the potential to be an interesting action scene.
Now, 4e have a ton of shortcomings that a lot of their fans are well-aware of it. The most common is usually related with a lack of out-of-combat tools for players beyond Skills (that are kinda too broad), Rituals (that many people ignore because of their monetary cost to cast), and general common sense ("I was on the army, so I know coats of arms", "My mother was an armorsmith, so I might know common alloys", etc).
However, if what you actually like are impressive tactical combats, no edition can match 4e's combat depth. Specially if you have a good DM that know how to use terrain features instead of the good old 10x10 empty room with some columns.
