We there in September and had 4 days of diving.
Best shore dives in the Westpunt area: Alice in Wonderland, with Ocean Encounters West, an excellent full service dive shop, right on site that offers boat dives as well. Also, Porto Marie, which was our personal favorite shore dive as the reef structure is fabulous! There is a shop on site for fills and tank rentals, don't know about other gear (we brought our own). You could easily do several dives there. Another decent beach dive is Lagun, not quite up to the other two but still very nice and as a bonus turtles are almost always seen there. Both Porto Marie and Lagun have nice developed sandy beaches with bars and restaurants if you just want to relax.
There is a boat dive that you absolutely should not miss, and that is Watamula. It is one of the most gorgeous reefs we have ever seen. There is another great boat dive, and that is called Mushroom Forest, with wonderful and bizarre topography.
Curacao is not a "big animal" destination. Lots of fishing and we saw no large predators such as grouper or sharks. The tropical fish population, however, is very vibrant. There are reputed to be some areas where you can see tarpon, but these are not on the reefs. We stayed on the reefs to enjoy that 100' vis, really beautiful.
Closer to town, the Superior Producer. We could not make that one because the shore entry conditions were very rough. We did not have time to attempt it by boat. By all accounts of our friends down there, one of the top dives. However, it can be deep and have currents. At your experience level, use caution. Any dive shop will probably want to give you a checkout dive before taking you on that one.
We did not do any diving down towards town as we concentrated on the Westpunt area, but there is supposed to be several great reef areas there as well. Our friends told us about"black rock" which is a boat dive but boasts 6' gorgonians. We are definitely planning to do that one when we return.
In general the shore/boat reef diving is very benign and excellent for newer divers. Very light currents, great vis, warm water, beautiful colorful coral and fish, everything you could want. There is lots of good information in this forum if you look in other threads. There are also a few Curacao natives that post.
In terms of topside things to do, the main town is the place to be for shopping, partying and fine dining. Westpunt is very quiet. No shops, no fancy restaurants (although the Lodge and Sol Food are very good eating). Lots of lazing on the beaches, some of which have bars and restaurants, and some of which are more quiet and deserted. There is also a national park and some scenic driving.
However, it is only a 40-45 minute drive from town to Westpunt so you can easily go to town for day or two and return to your home base afterwards. Driving is no problem on the island.