I loved Witcher 1 when I played it a few years back. Hard to put my finger on exactly why, because it's certainly not a game without flaws, but I found it immersive in a way I don't remember experiencing since the crpgs I played as a kid. The music certainly had a lot to do with it, with its folksy, wistful qualities. I guess I found something charmingly old-school in the awkward combat and inventory management as well. I really liked the choices and consequences part of the game, although they did me in in the end.
Like MysterD said, if you don't like the way things turn out you have to backtrack hours to choose differently, which I had been patiently doing throughout the game to get the narrative I wanted, because I knew I'd never do a second play through. In the last chapter though I finally got distracted and left the game unfinished, so it's sat there in my backlog ever since, preventing me from moving onto the second one. Just like Mass Effect. I have a problem finishing RPGs, apparently.
I think it's the way the atmosphere + bleakness of the actual TW series is that actually spoke to me. B/c the story + character development is done as a slow-burn to slowly build things later into something awesome, you can really soak into the Lore (in the Codex), the game-world itself, quests + side quests - all things I really dug of the series.
There is often not anything nice about this game:
it's as adult, dark & bleak as it can get. Always seems to be some manipulating of major events, conspiracies & political mischief going on. When other RPG's had "Good/Bad/Neutral" meters and things of that sort (often like Fallout series had Karma meter + BioWare games after BG had a Good/Middle/Bad Meter), TW just gave you choice + consequence - and made you often live w/ your decisions b/c you didn't feel like returning back numerous hours or so.
Most RPG's - make a decision now, see a result almost instantly....and you can quickly reload last save from few minutes ago to get a "preferred" result, if you don't like how things turned out. TW didn't go for this at all. You made a decision - live w/ it or go the hard route back numerous hours to change your result. B/c I'm lazy - yup, stuck w/ my decisions in this game series.
The other thing was - well, most games really sucked at trying to show actual sex scenes; push boundaries about nudity; and things of that sort. Most games...didn't go really there. And if they did - they weren't going for it the likes that movies would + could. Movies had no problem getting that R rating, loaded w/ sex + nudity. Movies always did - and probably always will - do this stuff way better than games b/c it looks more believable (b/c real people are involved doing the acting, in most instances). Most games, they'd either cut to black/fade to black when a sex scene was about to hit; not go for nudity; and not go for sex. When games actually did - things looked & were animated way off + came off as awkward (i.e. some of Dragon Age: Origins, anyone?).
At this time - Witcher series always seemed to actually do this stuff better than the rest of the pack. Games dev's and/or publishers were afraid of winding up possibly in AO territory, which meant you weren't going to find this game at your typical retail store (Best Buy, WalMart, GameStop, etc) if the game got AO rating. The publisher made them cut content out of the US version - i.e. also see what Atari did w/ Fahrenheit (b/c it got slapped w/ AO) and re-branded in Indigo Prophecy. CDPR fought to Atari tooth + nail w/ TW1 to get their game w/ nudity + sex all intact here in the USA (since Atari made them chop the content out of the original US version, not the UK Version) - and got TW1 re-rated by ESRB in the USA and all; and they succeeded.
About you not finishing RPG's - do you have trouble finishing long-winded games? If yes - you might just wanna take them in chunks, here and there. If you can find a worthwhile story-arc to stop at - do so. I know that often after 10-30 hours of something, I'm looking to play something else, to take a break from said long-winded game. Even if it means playing something short like Gone Home, in the middle of long-winded said game and/or some short-winded FPS (COD, anyone?), before I go back to said long-winded game. Just make sure, you get back to it soon - or, you'll likely never get back to it.