Ok, I downloaded it and played a few stages in DSMBL and DSII (Arcade mode). Here are some impressions. Just playing with the PS4 dualshock as I don't have an arcade stick for my PS4.
-Very low input lag. Feels the same as the X360 ports in this regard.

-DSII looks weird, somehow worse than the X360 version. The contrast looks too high and the colors look more washed out.
-I was disappointed they still do not allow us to input our initials in DSII, at the high score screen. Still no online replays either. Overall this "port" feels like it is just copy-pasted over from the X360 version.
-Very little slowdown in DSII except when you enter power up mode, it seems like a bit less than the X360 port that was already missing a lot! How they screwed this up is beyond me.
-DSMBL, in contrast, has MORE slowdown than the X360 port in power-up mode. They put back in the bits missing in the X360 port (e.g., the forest boss at rank 999). Some parts actually feel slower than the PCB.
Bad thing about both ports is that in the screen adjust you cannot fill up the screen vertically. They only allow you to move it up a couple notches then it stops (up to 102% in DS/DSMBL). Really weird, but something a patch should fix easily.
I know SPE and other top DS/DSMBL play-tested this port, which explains the better slowdown accuracy there, but it seems no one bothered with the DSII side of it, which is such a bummer because that is my favorite game of the bunch and we already have a half-assed port on the X360. So far, the X360 port is still better than this port of DSII.
