I mostly liked it, and thought it was a fun ride. Nothing major, nothing mind blowingly awesome, but thoroughly entertaining for 90 minutes, with a decent enough cast.
...Is it bad that I kept wanting to call the big bad Lycan, "Dyson"?
The action was decent enough, the scripting was surprisingly emotional at times for an Underworld film, and I suspect those scenes were the ones that JMS touched.
I am intrigued to see where they go with a fifth movie, and do honestly hope we get another one.
Like I said, not a lot to say. Entertaining, but doesn't leave a HUGE impression on me. I'd watch it again though.