I didn’t warm to it either… Interesting as a separate mini fan-film, but it seems out of place to me with the rest of Episode IV. I felt the same way about the end of Rogue One - while Darth Vader’s antics worked quite well in that film, they didn’t seem to flow naturally at all into the beginning of Episode IV where he calmly enters after his troops and does very little dirty work other than to pick up and choke Antilles one-handed.
Vader in this YouTube clip also lacks the stature of Prowse to be convincing; he’s barely taller than Alec Guiness. (That always irritated me at the end of RotS too.)
Bluto