Hi,
I'm an old player. My problem is, I always find sequels of great games I loved boring,
or somewhat not good as the first. It happened with Soul Reaver, it happened for NWN,
it started centuries ago with Doom and Monkey Island. My question is:

Do I have to buy TW2? Will it be enjoyable as the first?
I read it's almost a different game...

As is the case with most sequels, many things were changed. Some for the better, some not so much. That being said it's still a damned good game and as an old player like yourself, I'd still recommend playing it. Story is good, and continues where the first game left off, answering many questions (and opening up many more). Overall I think I prefer the first, but I didn't regret a single penny spent on the second one (pre-ordered from GOG).

The game-play of TW2 is very different from the game-play of TW1.

TW1 has the game-play of a classic computer rpg.

TW2 is, in my opinion, an action rpg.
It is a great game, but you gonna need to learn how to play it and until that happens, you gonna die a lot.

I think you should check it out by yourself.
This video-tutorial may help you to decide:
TW2 -Combat Basics
It's from the beginning of the game, so it isn't a big spoiler.

Okay, guys, you were both helpful, I owe you one.
I'll buy the game as soon as I get a laptop capable of running it.
Thanks

Don't underestimate the system requirements for it, I dont think a laptop will be able to play it well.

You'll need a very, very high-end laptop to play it well. I'd suggest conceding that some hobbies are just naturally expensive, building a decent desktop, selling organs or favors and getting a GTX 580 or similar high-end card, and playing the game as it was meant to be played. (For the most part, anyway. It still won't do ubersampling. Oh well...)

...but otherwise, TW2 is probably a better game, all-around, than TW1. The plot is much more intricate, with lots of fun political intrigue, lots more important but morally grey choices, and more bad guys and good guys alike getting what they don't deserve. Sex in the game is much less adolescent, much less of a Pokemon affair (i.e. 'gotta catch 'em all!'), even if some scenes show, er, quite a bit more than the little cards did. The writing and voice acting are much better: nobody sounds out-of-place or speaks with contextually bizarre intonation, and some of the voices are really exceptional. And a lot of the game is funny. Not a no-fourth-wall laugh-fest like Fallout 2, such that the whole game has to be taken tongue-in-cheek, but it's much livelier than TW1. Combat is different from TW1, and requires better reflexes and better planning than TW1 did, but it is probably more fun than TW1's system - one feels, at any rate, more free to watch the beautiful swordplay, since one needn't watch for a sword cursor to change to a flaming sword to continue a combo. And fights are certainly paced better than TW1's: you won't catch yourself thinking "Oh, joy - more drowners." (Except for one scene, anyway, that pokes fun at that aspect of TW1.)

It's worth mentioning that TW2 is way more stable than TW1. TW1 crashes like a fifteen year old girl in driver's ed. TW2 hasn't crashed on me yet.

If there's one thing I don't like about it, it's that it doesn't feel like a sequel to TW1 at first. I finished TW1 as a god of war, armed not only with the best weapons and armor the elder races could forge, but the skill to use them. I start TW2, and... that shiny mahakaman rune sihill that once ignored whatever armor was unlucky enough to be in its way now is only slightly better than Temerian general-issue sharp sticks? And I've apparently forgotten how to swing a sword so as to slash at several foes, and have to relearn how to do it? Well, whatever. It's a small price to pay.

Oh, and the lack of a modding toolset. But it's been promised; it will come...