His people are almost caricatures, which is quite an acquired taste. Sometimes that can go too far, but on the whole I've always liked his style. Lone Wolf doesn't feel right without his art in it, and I was really disappointed with the artwork in the new reprints from Mongoose; it has no individual style or character and is instantly forgettable. If you look back at the FF artists, you can easily pick out an Iain McCaig from an Ian Miller or a John Blanche from a Leo Hartas. And indeed, it's easy to pick out Gary's work from any other artist.
Here's an example of what I mean, using the Ice Barbarians (entry 216 in Caverns of Kalte) - Gary's original is on the left, and the new guy Rich Longmore is on the right:
