Unfortunately, the dining in Carlsbad is rather subpar for a moderate-sized town near an important national park. If you'd prefer an upgrade on the chains Denny's, etc., try:
The Flume Restaurant
1829 s. canal st., +1 575 887-2851. steaks, etc.; arguably the best restaurant in carlsbad.
No-Whiner Diner
1801 s canal st, +1 575 234-2815. classic diner food and a clean atmosphere; not open on weekends.
Happys
4103 national parks hwy, +1 575 887-8489. classic diner food and breakfasts; fast service.