Agree 100% with "Princess Frosty" & "Sulaco". Modern games look better, but half of the "more complex gameplay features" added - stuff like button mashing Quick Time Events, heavily scripted "railroad" hand-holding (for a "better cinematic experience"), unskippable cutscenes (both traditional and "micro-cutscenes"), reusing the same key for "contextual actions" (SPACE = climb / jump / swoop, etc), treating people like dribbling idiots with giant "quest markers" pointing out the obvious, unnatural looking over the top "head bob", random 1st <> 3rd person camera switching, etc, is precisely what people liked the lack of in older games...
I re-play a ton of old games still and whilst I agree the older engines are technically inferior, they had a certain "feel" to them that just "clicked" within the first few minutes of gameplay. Any frustrations after that were usually down to coding bugs that got patched out, not intentional sacrificial "design decisions" targeting a "broader appeal".
I think the problem with Thief 4 is that it'll never really have the same "feel" as the Looking Glass Studio's games (neither will a System Shock 3) no matter what it does. They did a pretty good "damage control" job with Deus Ex HR after the utter joke that was DX:IW, but the fact they were still seriously considering "XP Headshots" in "NuThief" at one point showed that at least some of the devs really didn't understand what the franchise was about, and simply went through every other modern game looking for popular gimmicks to "throw into the pot".
I'm on the fence over Thief 4. They did seem to go to great lengths to appease PC gamers with highly configurable options (best seen in Total Biscuit's good review), OTOH, that doesn't solve the linearity, claustrophobic excessive loading screens (remember the absurd "blue fog" in Thief 3 to try and hide the fact the game had been dumbed down and 80% shrunk to fit the XBox's 64MB RAM vs "Life of the Party" in Thief 2?) or "dumb AI" issues...
PS: Does anyone else find the "permanently outstretched arms" thing highly distracting in Thief4? It's like a damn zombie simulator...