-Does the UI feel PC-y enough?
You can use the mouse to select options. Q, E, and the mouse buttons are your primary action inputs. Controls are fixed with no options. You have to edit the binding files in the game's directory to change them.
-Do you play with 360 or KB+M? (Is the 360 necessary for the analogue sticks? + Rumble?)-
Keyboard. It does a decent job with the directional moving.
-Is there a good soundtrack?
You don't hear it often. You will hear mall or casino music in the appropriate areas. There is some rock/techno/metal stuff with bosses and some cutscenes which is decent.
-Does it look good at full res + high res textures and stuff? (Are the graphics options better than on console versions?)
The first is subjective but it has more graphics options in game. The pics I posted above are 1920x1200 with everything maxed sans blur and multisampling which were disabled. Resolution/refresh, vsync, multisampling, blur, zombie quality, shadow quality, texture filtering, and it has a baseline image to calibrate your gamma which is a must IMO. There are also more zombies on the PC version.
This game sounds good.... but does it deliver on the whole 28 days later/L4D-esque feeling?
None if the above. Outside of most cutscenes the game does not take itself too seriously.
(Does it play like Devil May Cry OR more like Dynasty Warriors?)
I guess more like Dynasty warriors with the moving and masses of zombies. Not as fast as DW and the control scheme is simpler.