According to SBJ http://www.sportsbusinessdaily.com/Journal/Issues/2013/04/29/Media/NHL-RSNs.aspx and based on data through April 21st, the Islanders showed the largest rating increase in the NHL this season (excludes Canadian markets, as well as Carolina and Nashville). SBJ's figure shows that Isles ratings are up 133.3% (in English, for every three people that watched a game last season, seven people are now watching).
The Isles' local rating (0.49) is still among the lowest in the NHL, but that reflects the diversity of the NY market. (The Devils are also in that group, as are both LA and Anaheim. Florida completes the lowest rated but that's because nobody watches their games!)
Given the importance of the Isles games the final week (and lack thereof for the Devils), I would expect the final season ratings to flip between the two teams, but as of April 21st, here are the ratings from SBJ for the three local teams:
- Rangers: 1.70
- Devils: 0.50
- Isles: 0.49