I played the first one through and loved it. I'm now playing Witcher 2 and loving it as well.
If your concern is the plot and back-story, I think you'll do fine just reading the plot summary on Wiki
As far as importing a save game, it carries over a little bit of money and gear, but nothing that gives a huge advantage. You'll have earned more money and better gear in a few hours anyway.
The biggest issue I can think of is in understanding the mindset of the character, the game, and the world. The Witchers are powerful warriors like you'd find in other games, but that's not what makes them interesting/unique. Their specialties are knowledge of the many exotic monsters and their alchemy with potions (and traps and bombs in this case).
Reading/researching about creatures would be optional codex/lore in another game, but here it is part of the quests themselves. Potions, bombs, traps would be optional consumables in another game - and I personally rarely use them - but here they're critical.
Many people are struck by the difficulty of the game, and it's usually because they're trying to sword-fight their way through everything. If you really make use of the traps, bombs, potions, oils, etc. you should do just fine.
Lastly, understand that the character Geralt is not trying to be a heroic soldier. Unlike in comparable RPGs, you're neither a great hero nor villain, just something like a tough exterminator travelling from village to village cleaning up their monster infestations. Getting caught up in politics and wars is anathema to the cynical Witcher who just wants to be on his way to the next job.
Push Letho away with Aard, immediately follow that with strong or fast attacks for approximately 2-3 hits, repeat the process until you run out of Vigor; when that happens, run away. If Letho puts Quen up, set a Yrden in front of you to tear it away and buy you some breathing room. Don't attack Letho up close unless you're absolutely sure you want to, and make sure you parry and attack only when he isn't. If you can stun him by parrying, excellent, but only parry when you're just about to be hit by one of his blows. Also, make sure you're using the Steel sword, as it's more effective against humans. You can also set up a few traps quickly if you wish, and ALWAYS dodge to the right just before the battle begins, so Geralt can shift away from Letho's Aard if that's his first move.
Best Answer
After finally beating the Kayran, here are some tips on killing the beast.
You need to trap the tentacles using the Yrden sign (The 4 tentacles with the slightly glowing, thicker part). You can only trap the 4 rear tentacles with the glowing part, the front tentacles of the Kayran cannot be trapped!. If you crafted a Kayran trap, you can use that one for the first tentacle, the location is highlighted if you have the trap in your inventory. You need to place an Yrden trap at a location where the tentacle will hit the ground. The easiest way to achieve this is to stand in the same location as the trap, once the Kayran lifts its tentacles, immediately roll to the side. The tentacle will hit the trap and you can sever it.
Avoiding the tentacles is important, a direct hit can do a lot of damage. Watch the pattern, you'll quickly notice when the Kayran lifts its tentacles and it is time to evade. Sometimes it also hits you from the side with a tentacle, but I haven't found what triggers this attack. You also shouldn't stand directly in front of the Kayrans mouth, it can perform an attack that poisons you (if you didn't drink the Mongoose potion) and immobilizes you.
You can also use the Quen sign to protect yourself from damage, but you have to time the casting right or you'll just be hit by a tentacle while or shortly after casting it.
After severing the third tentacle you get a quicktime event (right click, repeated left clicks and space) which will cause parts of the old bridge to collapse. The Kayran now throws stones after you. You need to go to the left and go up the fallen down part of the bridge that now leads directly onto the Kayran. And then you've finished this fight. Don't forget to loot the Kayran for reagents and crafting material.