Could have been a hit
I think if the script had been better written, the bridge scene not being the big ending (instead perhaps the hotel explosion and rescue).
With a budget double that of Star Wars, i find this hard to see why the special effects are awful. Yes Bisset, Holden and Newman were paid over $1 million but i think the lack of effects was the nail in the coffin.
Also the timing was bad, i think if this had been made instead of The Swarm in 1978