Kittonwy, are these the concept arts you refer to ?
http://www.neogaf.com/forum/showpost.php?p=9944073&postcount=1
If so, they are indeed beautifully rendered but compared to MGS4, KZ2, LBP, DMC, HellBoy I & II (the movies), Pan's Labyrinth (movie), I think they are lacking in imagination, personality and "sexiness". If they want to start from scratch, might as well expect something higher internally. What gave the R1 monsters personality was their in-game (AI) behaviour. I was never really attracted to the Resistance concept art (I don't hate them either).
I do agree that there were too many lost opportunities in R2 SP.
In R1, the monsters seemed to have deeper behaviour (Hybrids flank more effectively, menial will hug, bite and sometimes carry explosives, Stalkers will stomp all over the place in a level full of hiding places and debris, Titans will move more freely, etc.).
I feel that in R2, I am forced to keep my distance because my health bar is artificially made too short, I don't have many powerful weapons to take the hordes on. In effect, compared to R1, I was gimped to make the game fun (The enemies in R2 are mostly one-trick and so "far" from me that they lost most of their personality). Together with the fragmented stories, the R2 handicap gave me the feeling that something is missing throughout the game.
Even though I enjoyed the game, I felt somewhat constipated.
I believe because of that safety distance the player kept between himself and the monsters, the enemies were designed to charge repeatedly (or some say indefinitely) to make things eventful. It could have been more interesting if I am right in the thick of these battles like in R1. R2 SP has a few of these but mostly you have to fight strictly behind cover. The Chameleons should not be a one-hit killer, I should be allowed to duke it out with him for a longer period.
That said, I think the hilltop R2 Co-op fight far surpassed the best R1 level. It's the only place I felt threatened in shooters (like playing in an alien movie where all your comrades were murdered. It's "Game Over" if I died too). Amongst all the R1 and R2 monsters, the Hybrids (Augerer and regular foot soldiers) in R2 remain formidable. They are determined, vicious and extremely mobile -- given the right level design.
Overall, the R2 experience covers a wide range. If they can tighten the experience, I have no doubt that R2 > R1. And I disagree with Kittonwy's criticisms on HDR, shadowing and what not (Seriously).