It's been stated many times here and in other forums, games from '51-'56 are the pinnacle of the EM era just for the fact playfield duplication hardly ever happened, each designed playfield was radically different from the last. Also, 4-5 ways to win was the norm. Along with high scores, a points system and 2-3 other sequences were offered. What I really like on these games is your failure to bid for 1 sequence during the course of a game may find you within easy reach of 1 or 2 others, changing your entire strategy, or, going unnoticed until that special lite all of a sudden appears.
Once Gtb. Majestic appeared in '57, introducing the spin roto, most games afterwards included this feature. I personally don't like it as it takes up too much space both above and below the playfield, making it the centerpiece on just about every game it shows up, (and limiting room for other features). It's like Gottlieb's upper management got to the design team and told them to incorporate the roto into everything because, "We love it!"