Very nice job with this game. The theming of it was very entertaining, and the variety of obstacles kept the gameplay fresh. Most of all though, I thought that the learning curve on this game was just right, escalating in difficulty, but never at a rate to make the player panic. The game was difficult, and often frustrating, but not ridiculous, which in my book is a plus (yes, frustrating can be a good thing on occasion). You did a great job of teaching the player what each obstacle entailed before throwing it in with the others. And you were forgiving enough to give the player a life set for each level, something I, being a pretty terrible player, can appreciate.
one thing I would recommend, though, is doing something with that hard earned score. My suggestion would be to take one of two options: (1) set up a scoreboard for the newgrounds version of this game, so you can compare your score with others', or (2) make the score a sort of currency, so the player can, say, expand the size of the rail car to allow for more lives, but while making the car more cumbersome. Or, perhaps, purchasing upgrades to make certain obstacles "safe," so the player can relax a little.
Overall, I thought it was a very good sequel, and nice addition to the nitrome collection.