PAIN fans that found the Downtown level a bit lacking would definitely be doing themselves a favor by downloading this new level, though those that weren't convinced by the original's package will not find anything in the Amusement Park that merit the $16 purchase of both parts of PAIN. There are just better games with more content on the PSN to pick up for the $10 that the original costs, so unless you've bought them all, this add-on alone is not worth the total cost of $16.
Online play is still the biggest thing lacking from the game, so the only hope if for a future update to include that functionality to increase the game's replay value. Trophy fans will be disappointed that the new trophies do rely on your purchase of the Amusement Park and certain add-on characters, which is the worst offender of the young trophy system for requiring add-ons for more trophies. The trophies themselves are probably the hardest trophies overall to earn amongst all of the games with them so far, as they require you to unlock some of the alternative levels to earn some of them along with the add-on-based trophies, as well.