I had a similar problem when I moved to Singapore for work a couple months ago. Here are my conclusions.
The offer you got sounds like what the employer is obliged to provide for S-Pass holders and Work Permit holders. In this case, it will cover your medical costs of up to at least 15'000 $. If you are however under an Employment Pass, then this is an extra benefit that your employer provides you voluntarily.
I would recommend you to ask for the detailed information on the insurance, as their coverage might vary a lot. Health insurances here tend to come with a lot of caveats and might not cover some things such as pregnancies, existing conditions or STDs which would be covered in the EU. The maximum amount they cover also varies a lot. Another factor to look out for is the type of ward you will be eligible for (See here for different types of wards) and whether you want to use private or public hospitals. (Both are of excellent quality as far as I can tell). Also note that for outpatient visits to GPs your insurance might only pay for certain clinics on a panel list. However, in my case this panel list is so exhaustive, that I doubt I'll ever be further than 15 minutes from the closest clinic I can go to.
Now if you want to compare your maximum cover to the actual costs, I suggest you have a look at the list of average prices for hospital treatment of the Ministry of Health or outpatient charges at a public hospital. Note that if you go to a GP outside the hospital, this can be a lot cheaper. I usually go to a doctor in a residential neighbourhood (public housing) and the consultation cost is about 20-30$. Of course this will probably be higher if you live in a posh area.
So I'd say, definitely read through your policy very carefully before you decide whether you want to get extra coverage or not, take special note of exclusions and price limits. In the end only you can decide whether this is enough coverage for you or not.
As for prescribed medicine, you will very likely be given your medicine directly by your GP or your hospital. Quite interestingly, contrary to what I'm used to from Switzerland, you get the exact amount of pills you are prescribed in a ziploc bag instead of the whole pack, which makes them quite a bit cheaper.
Also contrary to what is common in Europe, you will in most cases have to pay medical bill first and then you can claim the amount from your insurance.
Overall I can say (after several visits to a hospital and a GP), that the health system is of very high quality, on par with anything you can find in Europe, and the prices quite affordable (compared to Switzerland at least). It is also very convenient as there are lots of GP clinics in residential areas and most of them run on a walk-in basis, so no need to take an appointment. Just (as with everything in Singapore), be prepared to queue up for a while.