I'll use room service, particularly after a long day when I just don't feel like going downstairs to the restaurant. Typically it'll be a breakfast or a late dinner - in which case I tend to go with the less expensive options like burgers, a sandwich, fish n chips, or a local equivalent outside the USA.

If I want a full, proper meal (i.e. something beyond the basics) I'll either go to the restaurant or go out.

Edited to Add: ok, I mispoke - it's been awhile, I can recall ordering full meals before like salmon filets or even a good filet steak -- this is clearly the exception to the rule. When I've done this, room service has always come with the full setup and no complaints about food.

I've had excellent room service meals and typically it is just as good as if I was eating downstairs in the restaurant.