I love the fact that such an excellent game is so popular and on such a roll but if it ever breaks into the top 3 or gets to number 1 I'm going to be extremely upset. I've yet to play the whole game but while it is great I don't believe it is worthy of toppling any of the top 3. And if people are so in love with SS2 why aren't they feeling the same love for Deus Ex ?
The place of a game in GOG's bestseller list doesn't have anything to do with merit or being better than the games below it and it's certainly no good reason to get upset about, IMO. Keep in mind that SS2 was quite hard to get a hold of due to the licensing issues, whereas the D&D games were partly still being sold in retail stores or for acceptable prices on ebay. Also, the D&D games are so popular and well-known that chances are a lot of gamers already owned them before GOG and not all of them would buy a second copy. SS2 on the other hand seems to have a cult following, but I wouldn't have known about it if it wasn't for the GOG community. So I bought it to see what all the hype is about, not because I like it better than PS: Torment. In fact, I contributed to making SS2 climb further up the bestseller list precisely for the fact that I didn't know it yet. As trivial as it sounds, the bestseller list is not a ranking but only an indication which games sell well at the moment, for whatever reason (and for some games the reason is only that they're extremely cheap, regardless of quality).
Anyway, I didn't know Deus Ex either, but what I do know is that it wasn't in the same legal limbo as SS2, so the circumstances are different. That being said, as a new player, I watched the intros and played the tutorials of both; the gameplay was very similar, but while SS2 managed to draw me in and make me curious right from the start, the story and setting of Deus Ex confused and bored me. (Just talking about my first impressions, I plan to play them both eventually and might revise my biased judgement which could also be related to my preferences in genre - exciting suspense horror à la Alien vs. geeky cyberpunk thriller à la Matrix.)
System Shock II really draws you more into it in the first 10 minutes, but than (in MY opinion) Deus Ex gains supirior to it:
Just cause you´ll proberbly replay the first mission after you´ve failed it the first time:
And you´ll see NEW possiblyties. And than again and again...
Sneaking around the guards?
Hacking into the systems?
Crawling through small tunnels?
Sniping an opponent from a distance higher than 1 kilometre?
Everything is possible in the first mission!
(Exept the things you need Augmentations for...)