I think Walter Pidgeon was badly miscast in this film. Just not believable in the role. Barbara Eden was beautiful, and acted her part well enough. No one else was at all memorable.
I remember the TV series spun off from this movie when I was a small child. I even think I had a plastic "Seaview" that would submerse and was great for playing with in the bathtub. Long time ago.
As for some of the other criticism I've read for this film: It's certainly unfair to judge special effects or science knowledge of 4 decades ago by today's standards. The effects were OK for 1961. Not great, but OK. As for the science, that was ludicrous even for 1961. There's no excuse. Also, the sub was awfully roomy. I understand that the navy refused any help at all for this film, so maybe the filmmakers just had no idea.
Overall, the film bored me. (And I'm a sci-fi fan.) Can't recommend this one. Grade: D-