This game is the reason I bought a CDROM-drive (yeah, I'm that old). This truly is a groundbreaking classic. And actually, this is the only game in my collection of which I find the soundtrack worth playing. It's great!
Through the years there have been many great games: Ultima Underworld, Baldur's Gate, System Shock, The Witcher, STALKER, to name but a few. But Deus Ex stands above them all. This is the one. This is a no brainer: if you don't have it yet, get it. Don't waste time reading reviews, play it. You know you want to!
I know Gothic3 is a kind of love-or-hate it affair. Yeah sure, it has its problems, but I just love it. One of the best RPSs ever, great story, great setting, great feeling. If you can overcome its shortcomings, than you'll love it too.
I really, really wanted to buy this game on GOG. But when Steam made me an offer I couldn't refuse (can't remember exactly, but it was less than 6 euro), I bought it over there. Wherever you buy it, it's an absolute classic. For every RPG-fan, it's a no brainer: get it! For all the rest of you, since it's available at GOG for a GOG-prize, it's a no brainer as well: get it!