It was a very well designed vehicle that rightly thought from tactical needs backwards to design. However the totally fixed gun was I think a triumph of doctrine or engineering fetish over common sense: a vehicle that becomes useless if immobilized is a poor investment.
Of course those were the days before reactive armour, but it does remind you that low profile/concealability, speed and maneuverability are the most important aspect of AFV survivability.
https://en.wikipedia.org/wiki/Stridsvagn_103