Awesome visual effects in that episode. The seamless integration of old and new on a TV budget, absolutely fantastic. And the physical TOS/DS9 Enterprise looks a million times better than the CGI TOS-R Enterprise.
The only problem with this episode is the soundtrack. Especially in the fight scene in the casino, it gets way too dramatic.
And while I liked the mystery about the Klingon ridges and Worf being uncomfortable about that (I absolutely hated that Enterprise had to ruin that), they should have turned Worf into a ridgeless Klingon the moment they traveled through time. And nobody should have cared.