Strong was in makeup. The other choice would have been foolish, which is not to say that it's a foregone conclusion that they wouldn't have tried it.
To do that stuff as well as the Na'vi in Avatar
is still a challenge and I don't think anyone but WETA has a chance of getting it right, at this point, on major characters. There's a lot of potential in the future for the Guardians as individual characters in GL, but really not if they continue to do them as they did here. IMAO.
OTOH, the mask that so many wrung their hands over for so long works perfectly in GL, as do the CG costumes. Yes, they look weird and unlike clothing, and they're supposed to...but man, effects have come a long way from Christopher Reeve flying toward Boulder Dam in a chartreuse Superman outfit because they couldn't color correct against bluescreen closely enough.
Mark Millar evidently hates the movie, which is another strong point in its favor.