I feel Geoff Glover is not convincing

I watched The Guns of Navarone (1961) and Geoff Glover was one of the parts I kept noticing. Many moments pass very fast, and I do not remember much after them. The role needs more detail, but the performance stays on the surface. Some emotions are too simple, and I cannot believe the character enough. For me, it does not feel very real in many scenes. I do not hate it, but it did not pull me into the story. I remember both the good parts and the parts that did not work so well.