Really happy with these figures, it's a near perfect release and when considering the price point; it's beyond all expectations.
I made some minor tweaks, but thought I'd share something very doable that I think makes a big difference to Robin.
I wasn't too jazzed with how thin his tights were as his mechanical looking knee joints were the only big distraction. I was thinking about padding them out with cotton wool or saran/glad wrap or something. But I thought just an extra layer underneath might solve the issue. My partner's got an extensive vintage fashion doll collection and she found these for me (she had a few, but these were a nice skin tone).
There's no tag on them but I'm assuming they're Barbie or an alike, the length matched Robin's legs very nicely and went on without an other modifications. It was quite a bit of effort to get Robin's costume off, it's very form-fitted and took lots of small movements to get it to clear his hips. Also, his utility belt is glued at the back, I had to slice through the joined layers it to get it off but it reattached easy enough with some strong double sided tape. I did need to trim the ball joint that goes in the ankle connection slightly to accommodate the extra layer, I decided this was a better option than trimming the innner tights and it made the joint a little bit tighter as an added bonus.
The end result is the joints are still there but have a more rounded and organic looking edge, and most importantly, aren't a distraction to my eye anymore. The extra layer stops the shine of the plastic showing through as well, which is a nice bonus.
I'm sure you can pick some doll pantyhose/leggings up off eBay for not much money, and aside from the belt trickyness, it's a pretty easy upgrade.
The only other modifications I've done is taken in the sides of Batman's trunks and trimmed the excess and brought the cape material in to cover the clasp with a few stitches.