It was a blockbuster trade, for sure, but obviously St. Louis wouldn't have made it if everyone knew at the time how much actual value they were giving up. The main thing was Ronning, I think, who was just seen as an undersized power play specialist and had been playing in Italy not long before – it was his emergence as a key player that was probably the biggest surprise.
The "Life Line" generated buzz right away, but when the trade was announced no one thought it vaulted the Canucks into contention or anything. I still remember very clearly the "Outlook" portion of the NHL Yearbook following the 1990-91 season, which probably sums up the bounds of optimism at the time. The opening sentence read, "The Canucks' goal of playing .500 hockey may not be that unrealistic."
When they were in first place right from the hop in 1991-92, nobody thought it was going to last. (Once Bure arrived and the Canucks had a threatening second line with Larionov and Adams, that began to change, of course).