Based on stats, you'd have to say he was consistently pretty elite from mid-1979 to mid-1985 (1 season in Atlanta, then the first 5 seasons in Calgary).
He ran into some injury problems that limited his totals, but if you pro-rate his scoring paces to 80 games, the stat-line might have looked like this:
1979-80: 93 points (actual)
1980-81: 131 points (actual)
1981-82: 107 points
1982-83: 104 points (actual)
1983-84: 96 points
1984-85: 103 points
...which is pretty impressive, but, given that this was the highest-scoring era in modern hockey, he's "only" 8th in PPG over this period (not counting M.Lemieux's one season). He's also a -31 over this period, worst of the top-19 scorers over this time frame.
His WHA numbers look impressive, but those 107 points in 1978 placed him only 4th (!) on his team in scoring. And when he became the main-man and top-scorer the next season, the team dropped 20 points in the standings.
Then, as someone noted, his NHL playoff numbers are underwhelming to say the least. If not for that late-career run with Edmonton (playing on a line with Messier & Anderson), his playoff stat-line would have shown 33 points in 38 games and a -10. That's actually pretty terrible in that era for a guy who was a 100+ point scorer on a competitive team.
Other than his '87 run with Edmonton, I didn't see the guy play in his prime (and even by '87 he was probably past his best years), and I wouldn't want to speculate too much based on nothing but stats, but given those stats and his reputation among peers, I do get the impression of an extremely talented but somewhat aloof player who was not the kind of guy whom you'd bank on to lead your team to victory.
Still, 8th in PPG over an six years period isn't shabby. But is that in itself worth a Hall of Fame ticket? I say no.
