I'm not touching HR because the first Deus Ex is my favourite game and has a lot of great memories for me and after IW I don't need to take it any further. For me, it begins and ends with the first game.
IW was awful. No atmosphere, no soul, no humour, no meaningful links to the first game and none of the little touches that made the original so great. Not to mention the dialogue and cutscenes are wooden as hell. Deus Ex was the gameplay over the graphics and game mechanics, IW was the other way round. All the time was spent making ragdoll corpses and stuff. I genuinely struggled to complete it because it was so dull.
I've completed the original loads of times, a different way each time too! The funny thing is about DX, there's a lot of stuff that's a bit ropey (dodgy accents, conspiracy theory overload, etc.) but it shines as a game that totally draws you in that makes you care about what you're doing. How many people played the game a certain way the first time and then realised that they were 'wrong' to have done that, or that thing that happened that you wish didn't could have been prevented? (trying not to spoil anything ;-)
The guys who made IW even realise how much it sucked. This video is really interesting: http://www.youtube.com/watch?v=MGIdYl2oN74
I don't really know much about HR, but I hear it doesn't have a lot linking it to Deus Ex and after IW I don't really want to check it out. If anything, it's catering to the mainstream that killed the potential of the sequel, among other things. It's not that fans' expectations are too high, it's that after the travesty that was IW, a lot of people are wary of that same disappointment. I know I am.