Very impressed with this Metro system and daresay it might be one of the best in the world. I've…read morealso used public transit in Tokyo, Taipei, Berlin & Brussels and those were great too. The British Tube, NYC subways and BART/MUNI have a lot to aspire to when it comes to Metro systems. The Danes know how to get it done right.
The Metro here runs on time, and no drivers for the trains, which is pretty neat. Every station has digitized schedules so you know when the trains are running. And they are on time.
You can either buy one trip tickets or look at options for 12 hours or longer. And you can also get a City Pass which gives you access to the metro and buses up to 120 hours. Just check on the DSB website for your needs and the system is self explanatory.
What I love about Denmark is that while everyone usually speaks Danish, there is always an English option. Every single website I went to related to my Denmark travels had an English option. That's pretty amazing.
The one important thing to note is that while you can't really scan your passes to get into the metro, don't be fooled to think that DSB authorities are not checking fares.
I traveled to the airport a few times and a few times, attendants were strictly checking fare. In fact, my train ride for the last time to CPH airport, my fare was checked twice.
I read some other reviews written here and if you don't have proper fare, you will get a fine for hundreds in DKKs, so totally not worth taking a risk at all.
The trains are very clean, well run, stations also clean and signage/schedule are all easily understandable. This is the gold standard when it comes to Metro systems.