To be fair, programming games like this on an 80's computer would be much harder since you couldn't just do everything in a scripting language and not have to worry about CPU cycles.
There are other 'unfinished' games that are nevertheless lots of fun to play.
It's amazing: lots of people will insist that modern games need lots of polish and awesome graphics in order to be any fun, but it's certainly not always true - at least not for certain audiences and certain games. Evidently, sufficiently engaging mechanics and 'overall experience' (which is a very broad category, of course) can be enough to give players what they want.
With the Humble Bundles and Steam (and a lot of AAA titles going for console releases first or only) there has been a real surge in indy games the last 5 to 10 years.