Assuming your son is not some sort of loser geek and more like a regular person, an iPad (particularly one of the new ones) will probably delight him beyond all expectation. They work just fine with Windows machines.
Flavacraze's view is ... unique. There is a very good reason why no competing tablet has ever sold 1/1000th the number of units the iPad has. Cheap tablets are exactly that ... cheap tablets. If we were talking smartphones there would be some valid competition, but in tablets there are two choices:
Real tablet: iPad
E-Reader only: best bet is a Kindle
But don't take my word for it:
http://chitika.com/insights/2013/Q3-tablet-update
Check out that first chart. Note that this is based on actual real-world usage, not inflated "shipment" numbers from companies that won't reveal end-user sales figures.
Flava is also incorrect that iPads can't play, for example, .mkv movies. He probably meant that the built-in video app can't (until the file is converted), and this would be true. However, there are a bevy of video apps for the iPad that can play pretty much any format under the sun -- including one your son has likely heard of, VLC.
Buy with confidence!