A man can see any part of his wife, yes.
However, most women feel insecure about their bodies regardless of what part of the world they are from. A good husband would work on getting his wife to feel comfortable enough and at ease to want to show her body to her husband. A bad husband would get "frustrated" and start thinking of other women.
"maybe her pretty sister would be more free in bed" - This is not an answer to your question; it is misleading you. As an analogy, consider that maybe your brother would please your wife better than you would. There are enough "maybes" to get people to commit great evils. And this is why the Prophet (ﷺ) said, وما شاء فعل فإن لو تفتح عمل الشيطان ("your" if" opens the (gate) for the Satan") - Muslim 2664. So don't think "what if" and "maybe" and instead appreciate what you have and seek to derive maximum benefit from it.
From what you've described, she is fulfilling your right to having intercourse. She is doing what is required of her, from an Islamic perspective. If you want to go beyond where you both currently are, then you should start working on reassuring her, getting her to relax and be comfortable in these things without adding too much pressure. Some men are sweet/charming and have a natural ability to make women feel comfortable; unfortunately it seems you do not and will need to work on this.
Hope this helps, somewhat.
