I've been on COH for a little over three months, but here are my suggestions.
Existing TF/SF
General:
The problem with many of the TFs, especially the orignal 6 and the shard TFs, is that we have multiple repetitive missions where one would do.
Take Citadel for example.
We have 2 kill alls, followed by a kill boss room, followed by fetch, followed by 2 more kill boss rooms, followed by a hunt, followed by 3 kill alls followed by the AV.
Ideally, you could shorten the TF by just having one kill all before the AV because storyline wise you are doing the same thing in each of them, so its just padding to have more than one.
Or Doc Quarterfield: a hunt then rescue, 3 more hunts, kill boss, a hunt, kill boss, 3 kill alls, 2 kill targets, kill all, kill target, kill all, kill boss, kill all, 3 kill bosses and a kill all.
Lazy! Even the souvenir reads like a check list. You could probably chop this TF in half or even a third, and still tell the same exact story.
Even beyond that, the old TFs suffer from repeating objective syndrome, there's no reason why TFs should be almost nothing but kill, kill, kill.
Specific:
Positron:
Can be done in 5 missions. One each for COT, Clockwork and Vahzilok where you uncover their plans for the dam, at which point there's a mission which all three plans come together(a rescue) and the mission at the dam substation.
Synapse:
A pretty decent TF. Still where we have 3 kill alls in the substations, we only have one. Instead of checking 3 warehouses at the end, we only have the final warehouse, and move Babbage ambush to save Fema Worker one, as sort of a "warning" from the clockwork king not come near.
Sister Psyche:
For a task force that concerns the ZIG, there's a distinct lack of the Zig. Have the sonic devices be in a sewer beneath Brickstown and the final mission be in the Zig itself(Clamor tries to break the convicts out by force). While Brickstown is a level 30 zone and the TF is 20-25, you could get around that by using a train.
Citdal: Explained above, but essentially there should be one factory to shut down at the end. Any more is just padding. Switching up the mission objectives and tile sets can't hurt.
Moonfire: Compared to Hess, this is an inferior TF. Could be condensed, but not as bad as citadel.
Katie: Unlike every other TF/SF with an AV, this one has its at the start. While its a great AV fight, once its done, TF is a cakewalk and done in ten minutes. Adding an AV at the very end couldn't hurt. Like when you get Katy's soul to lead her out, suddenly Jack in Irons ambushes you at the entrance.
Numia: Some people don't like the hunt portion, I do but lessening the number can't hurt.
All Shards: All need to be condensed and take place in the shard itself.
Sarah Moore:
The 4 seals can be in one mission.
Doc Quarterfield: Explained above, but this thing is pure laziness(nobody who wasn't wouldn't have though this was a good idea.) Condense or delete entirely and re-do.
Augustine: No need to be running 8 million place. One monument in each zone could do.
Faathim: Get seven keys in own mission, then use said keys in seven different spots. Zzzzz.... At least this one has AVs sprinkled about. Probably would need to re-do completely since this has to do with Shard Lore directly.
Terra Volta Re-specs: Waiting around for thirty minutes is extremely boring. Cut the time down to 15 minutes max.
Silver Mantis SF: Should not be found on SG computer. Make her an actual contact in a zone.
Lord Recluse SF: First mission is too chaotic for its own good, could stand to be streamline a little, fewer objective. Final Mission should have Phalanx spread out so we don't have to face 8 at once without a Dom.
New Strike Force ideas
The villain 10-15 SF could and probably should star a Cap Au Diablo faction, like the Goldbrickers or Luddites, luddites especially, since there is very little done with them.
The 30-35 SF could be one of two things, First we fight a hero faction, probably a new one, with a hero at the end. Or we have a Tsoo or Family SF, Tsoo especially since we don't fight Tub Ci ever but should.
The 40-45 shoudl either be Malta/KOA or Carnies. If KOA is going to get in a SF, their caltrops should be delt with.