Let's compare them directly. Here's a list of their comparable features. Feel free to add any if I've left any out.
Indiana Jones
1. No skill shot
2. 9 physical modes, 3 video modes
3. 1 mode start
4. Ramps change the modes
5. 2 ramps
6. Hand of Fate award
7. Plays vertically
8. Path of Adventure
9. 2 ball multiball/Ark, stones, grail multiball
10. No equivalent to powerball
11. Hurry-up
12. Extra ball: lighting all friends/Path of Adventure/crossing rope bridge/Hand of Fate/Raven Bar
13. Loop Jackpot
14. No combo shots
15. 6 ball eternal life wizard mode
Twilight Zone
1.Skill shot
2. 14 physical modes
3. 2 mode starts
4. Bumpers change the modes/slot picks random
mode
5. 2 ramps
6. Camera award and spiral award
7. Plays vertically, plays horizontally from left to
right, plays horizontally from right to left
8. Power playfield
9. Multiball/Powerball Mania
10. Ceramic Powerball
11. Fast Lock Hurry up (mode)
12. Extra ball: spiral award/Lite extra ball(mode)/Super skill shot/Robot ramp/dead end
13. No equivalent that I can think of
14. Combo shots
15. 6 ball Lost in the Zone wizard mode
That's about all I can think of at the moment, but for me these are already plenty of things that contribute to a worthwhile experience for both machines. And from my count, getting extra balls on Indy would happen more frequently. As for the robot ramp, I believe it's 10 ramps for the first extra ball, then 45 for the second. Shouldn't be too easy.