What make a good sub enlcosure?

So what would make a good enclosure? I'm just waiting to order the driver and amp till I have all the money to do so but I have made it out of MDF with a strong rigid construction it's ported I have made sure everything is air tight elsewhere and is made to the exact volume of the desgin I used in WinISD and the port is the correct length and size too.

What else could there be?

I ask the question because I once had a philips £50 2.1 set and despite the sub being only 6Wrms it did and half make some sound and if I could get this sort of quality of design I think that I will be able to make a damn good sub!!

Just wondering for future to help my designs, probaly should of asked this before I started! :)

Thanks
Boscoe