Seem to remember that the WHA was ahead of the NHL in bringing over European talent, including Vaclav Nedomansky.
The Hull, Hedberg & Nilsson line was called the best line in hockey for a while.
Gretzky, Messier, Goulet and several other future NHLers started their careers in the WHA. NHL draft was for 20 year olds at the time but would soon change when the leagues merged.
More then anything, when Bobby Hull signed to play in the WHA it changed salaries around the NHL. There was a lot of competition for players, teams were forced to ante up or risk losing their best players.