Well I reckon the first instalment is the best so you're in for a treat
Spent two or three hours on it last night and I think you are right mate.
Even though the graphics are slightly less refined (obviously) and the climbing mechanic also feels slightly clumsier, the way the enemy moves is far more challenging and it is harder to just beat them up if you run out of ammo. And I don't remember ammo being a problem at all on UC3. Overall it definitely feels the hardest of the three so far and great fun. I think it will have to go a long way mind, if it wants to beat UC2 in the environment stakes. Some of the settings in Amongst Thieves were beautifully detailed whilst still remaining easy to look at.
Anyhoo, in about 10 hours time I will be looking for a similar experience elsewhere and don't really know where to look? A UC4, PS4 launch title perhaps? Then I can see if playing in the present tense is all that it's cracked up to be.