Yes, this episode rocked! Well, I would say it's cool, but that might come off as a pun.
Ice Warriors have always interested me, and this episode sure didn't disappoint. It updated the Ice Warriors while staying faithful to the original design and didn't come off as cheesy. Definitely not an easy combination, but they pulled it off here. Hell, they even managed to make the clamp hands they had in the classic era seem plausible despite the fact this Ice Warrior didn't even have them. Skaldak himself was also a great character who I hope returns in some capacity again.
The story itself is somewhat by the numbers, standard stranded people being picked off one by one. Although the setting of a Soviet submarine makes this seem fresh, and all the movie Soviet tropes are a delight to watch in this sci-fi story.
David Warner was rather underused, although his character was amusing, a source of comic relief that wasn't distracting. But at times it seeme he was just shoved off to the side. Maybe that was intentional, convey that his character is an outsider among the sub's crew. But still, the guy is a great actor and the character was great when he was used, it's just a shame they didn't get more use out of him.
Nitpick: the captain has four stripes on his uniform, which means he is an O7 captain. However, my understading is that submarines usually have an officer with a lower rank for its captain, like a Commander or even a Lt. Commander. Or are things different in Russia (or were different in Soviet Russia)?
But yeah, amazing episode. Doctor Who is on a roll this year.