Here we go.......Karloff's Mummy is excellent, yes a bit slow, but it was 1932 sound had only been used a for couple of years. If you want fast paced movies forget the black & white era. If you like great movies dig all of these out. If you are not sticking to Universal you must watch the 1945, Karloff and Lugosi film, The body snatcher by R.K.O. possibly Karloff's greatest performance.
The Doc has named a few I must add The Raven, Son of Frankenstein, infact the whole Frankenstein series. Maybe some fifty's stuff Tarantula, This island earth, Them, Creature from the black lagoon, there is a big list.