I bought mine at 4am this morning when I came back from the pub. (Was a little worried I'd pre-ordered the hard copy at first as I couldn't find the download, but having sobered up today I've found it ... and it's Great.)
The Captain can be created in a variety of ways to suit your style of play, and you have to think carefully about when and where you use his abilities. He adds another dimension and more flavour to the game and doesn't unbalance it.
For me the 'best' thing about him is that you have to pay him each turn (from your treasure) to stay in your Warband, and the better he gets, the more he costs. So while he will advance like a Wizard, it's effectively at the expense of the Wizard. So your opponent might have a super duper Captain, but less gold available to purchase increases for his Wizard.
Some nice Scenarios in the PDF too. All in all a very well thought out addition. Good work all.
= )