Just wanted to add my 2 cents to this, since it's been brought up.

The concept of forest-dwelling, very diminutive, furry critters that are able to kick Imperial Troop's butt using primitive weapons was fine in itself....but did they have to end up looking so damned 'teddybear'-like?.... - http://images3.wikia.nocookie.net/starwars/images/b/b7/Ewoks-endor.jpg

I just wish that more of them had the kind of facial look (and headgear) that 'Teebo' has as we first see Luke and co. surrounded by the Ewoks. The fur that overlaps the top of his nose is a detail that I'd have liked to have seen on the majority of them too, as I was never keen on how prominent the noses look on the final Ewok costumes. - http://images2.wikia.nocookie.net/starwars/images/thumb/4/4f/Teebo_rotj.jpg/250px-Teebo_rotj.jpg

Maybe a bone / tooth 'adornment' sticking through a nostril on a couple of them would add a little something?

But the main thing that I reckon could make them look just a little bit more 'fiercesome' overall, would be to blacken out some of the ridiculous 'chipmunk'-like teeth in a few of them, and just give them a couple of upwardly protruding teeth from the bottom of their mouths instead. Here's a couple of examples of something along the lines of what I mean -

http://swyattart.deviantart.com/art/Wolfman-2009-136133505

http://brainfuel.tv/postimages/king_kong.jpg

Maybe some deeper-sounding noises and dialogue would have improved things too, along the way.

I do happen to like this particular ewok illustration though, which has an 'eye-patch' added. That would make a neat addition to one of them too. - http://starwars.wikia.com/wiki/File:Ewok-SWGTCGAoD.jpg