Nice to have the free preview, but it won't change my mind on how I watch hockey. I've had the league's streaming service for two seasons, and I couldn't be happier with the picture quality and availability. Allows you to start from the beginning of a game or go live, just like MLB's. (I believe the NHL uses the MLB engine.) It's also cheaper than Centre Ice, so I don't see myself switching for next season.
Starting this season, if you sign up for NHL Center Ice on DirecTV you also get full access to NHL.tv. (Authorized by going to http://nhl.com/activate ) It's worth noting that DTV's CI package also gives you NHL Network in season, regardless of your primary programming package.