If it seems 'pretty loose' I would guess it is 'too loose'. There will be SOME slack, but the more you have the better chance of it coming loose (which you know, and don't want

). I would say if it looks like you could easily install the chain if you removed a link, then you have too much slop.
The 1/2" rule is a good rule, but I have always had a hard time measuring it easily.