He was a good finisher whose particular skillset fit nicely on a great line with Savard and Larmer.
Under-rated? Not really.
He had his peak years in the highest-scoring 5-year period ever, and when you look at adjusted points, his 4 best years are 69, 59, 55, and 49 points. For a first-line player playing with two elite talents, not all that great.
When he wasn't playing with those two players, he never established himself as anything more than a 20-20-40 player from a 2nd line.
Could do two things really well - fight and finish chances. Otherwise, he was a very incomplete player who didn't skate very well, wasn't good defensively, wasn't a good playmaker, and was very injury-prone.
Better player than, say, Perry Turnbull or Paul Holmgren, or just better linemates/situation?
Statistically, when you look at his best years, they don't look a lot different from Neely/Tkachuk/Gillies/Shanahan/Roberts, but he wasn't close to as good as any of those guys.