At the start, this game didn't impress me much. An everyday FPS without much innovation. I also thought the main character "Mr. Jensen" was quite a dork, trying to be Matrix Neo.
Then something changed. I discovered the awesome level design and the world got more and more depth. A few puzzles started to appear which needed more thought that I've seen in any other FPS, and then ... I stopped playing it as an FPS.
It is claimed that you can play this game any way you want, but it is certainly most fun trying to get through levels without being seen at all. You will notice quite soon that once 3 or more mobs engages you, there is little luck in surviving. Best way to get through a level is always through alternate routes and not being seen.
Then comes the problem: bosses. Deus Ex has been criticised for not having enough interesting bosses, but the real problem is that when you've customized "Mr Jensen" to be the ultimate sneaker, you are forced to go full frontal attack in boss fights. There are no good alternative routes here and one of the last fights took med 43 minutes of kiting the boss around the map, always staying out of sight. I don't find that very fun.
I payed 9.99€ for this game, and it was totally worth it. I didn't expect much and got surprised that it was as good as it was. This is a quality game, almost the whole way through and in the end, even "Mr Jensen" becomes the cool hard ass that he sets out to be.
All in all, a great game!