If you dont learn the rules and the tips of DP, you can think "its meh... Not for me". But when you understand the rules, the tips and the strategy to adopt, you can only say "wow this game is really great"...
IM is a great pin, competitive pinball. You must have it in your collection because it give pleasure each time.
But clearly, DP give more fun, more strategy to have, more depth.
I have both, its clearly the best choice if you have the money. If i need to have only one : DP clearly.
DP is bad ranked in the top 100 because a lot of people do battles without strategy... Its just the last thing to do. And so they give a bad rate...