Thanks -- it does feel slightly different than "a good service" in English, but is that not the case in Polish?
Example: in English, if we found out that our hotel offers free dry cleaning, we might say "that's a good service." But we would use "that's good service" when we're talking about how quickly the waiter brought up room service or how easily the front desk changed a room we were unhappy with. It's as if "good service" refers to the people serving us, whereas "a good service" refers more to the activity being offered.
If it was about how the people 'serving' you behave, I'd definitely change the word to 'obsługa'.
- Obsługa w tym sklepie jest fatalna - The service in this shop is terrible. The shop assistants are rude, and they don't even have these fancy Ralph Lauren hats in stock.
Usługa is in fact more like dry cleaning and things like that.