Only reason I don't is that tends to result fights getting tedious because they take so long.

Again Frost Trolls are actually nothing compared to the Majority of the different types of enemies that you can encounter.

they kicked my ass when i foolishly tried to block their attacks, but once i got their pattern down (which included alot of random tantrums... those whacky trolls ), even my slow-ass 2-handed warrior could dodge their every attack and kill them quickly.

their difficulty comes from the fact that you can find them anywhere at any level though; draugr deathlords only show up when you have a legendary ebony greatsword and can show them how a FUS RO DAH is really done, but frost trolls can show up right after you've looted your first iron helmet.

now you know whats a real challenge? after youve just killed a blood dragon and are in desperate need of recovery, the giant the dragon was initially fighting turns to fight you just as youve wandered into a frost troll's territory. THAT was a fight to remember.

As other people have said, you're playing on adept.

I took one on yesterday on expert and he killed me the first 2 times. 1 or 2 quick hits and your toast. Luckily I like a challenge and got mine back!

It depends on your combat focus and level.

My level 4 mage could take that one on because it couldn't hit me playing rock tag, and it's susceptible to fire.

My level 6 warrior decked in heavy armor would get killed in 3 hits and could not get past the regeneration with hit and runs between its attack patterns. So he had to leg it.

Archer? EZ PZ... stand on a rock and shoot it full of holes.

It wasn't until about level 10+ Dwemer equipment that my warrior could take one on if you fight smart instead of slugging it out. (basically inbetween its attack pattern, do a 2H power attack, and once you connect spin around asap so your momentum from the attack moves you away from it)

That means nothing when many enemies have many times the HP and damage output.

Anybody that thinks Frost Trolls are one of the most dangerous enemies in the game are in for a serious wake up call when they encounter enemies that are actually dangerous.

Try no shield. If you don't have a shield they are atleast 25% harder.

Troll ? Bears ? Annoying enemies ?

Well usally those beasts are close to a cliff so the first dragon cry I learnt (the one that bump everything in front of u) at full power ..... OH GOD a flying mob !!! HAhahAHAHA , broken kneck ... let's loot !

try fighting one as an unarmored mage at level 5. You can douse them with fire for a good 20 seconds before they die, but if they hit you just once, you're dead.

Ok Harkle you have pretty much stated the same things over time, and so have other posters of this forum.
The reason why people find the trolls challenging is~
1.) they can be encountered at any level, and because of the game being still new people will be a relatively low level when encountering them. For this reason they get the label of being a challenging encounter.
2.) They have a random attack pattern making combat sometimes hard for people who don't have high armor and or health because they can't afford to try and figure out what the readying animations for each attack is.

And to respond to the "wait till they see the other creatures" you have stated, well first impressions are hard to forget as well as as stated low level encounters of trolls are hard because you are low level. The encounters you refer to are at the point the player has leveled farther as well,

Fight one on adept difficulty with standard (not upgraded) gear, or novice level spells, below level 10 and you'll have a different idea. I myself got my ass whooped (level 5) doing just that, but after returning 15 levels later with much better gear/skills/perks I cut him to ribbons in seconds.