What I Liked: The (2D) animation, can't fault the plot for being unimaginative, both Japanese and English dubs were amazing in their own right, great adaptation (as far as I can remember), the soundtrack.
What I Didn't: 3D animation could've been better (especially on Graphinica and Kelmadick's part), some of the insert song choices were off-putting (only good one? "Akuma Stocking" in Episode 5.), plot's a garbled mess with more (dumb) twists than a box of knotted-up cables, comedic scenes felt jarring and out-of-place.
Final Verdict: While the plot looks ridiculous on paper and on screen, Hellsing Ultimate still makes for a highly entertaining (and pretty) piece of occult action. Just be prepared for lots and lots of bloody battles and dramatic monologues.