Define successful-
In terms of operation, it seems to be a sucess already. The "vehicles" (to quote the media) are running, and seem to be carrying a decent amount of passengers. I understand there have been some schedule keeping problems, partly because of overcrowding and taking too long to load. I also read in the Trenton Times that there is a problem with one of the earliest morning runs not making an NEC connection. I'm sure all of this will be worked out, in time. The River LINE (and why that capitalization?) has been running, what, only ten days.
As to the overcrowding issue, on another thread someone suggested running longer trains. They have been operating mostly two unit sets, which is all they can run, as the platforms are only two units long. To run three units would requre double stopping at each station, and perhaps adding conductors to handle doors. I suspect that many of the riders this week have been casual riders, wanting to see what the River LINE is like, and that the numbers will level off.
In terms of success financially, never. This is a billion dollar project, and selling tickets at $1.10 each will scarcely put a dent in even the debt service on that kind of money. But then again, I'm not aware of any public transit that makes money. Not Amtrak, NJT, SEPTA, the MTA, etc. None of them-
Friends and I have been having a discussion about this, on and off, over several years. It is time that we, in this country, start to accept transit (all of the agencies above and more) as a public service, and be willing to fund them accordingly. Amtrak may never make a profit, but neither will the Army, Navy or Air Force. The military, or the government, isn't expected to make a profit.
Your local police force isn't run for profit, nor is the Interstate Highway System.
We just have to learn to accept the fact that certain services have to be maintained, and hope that the people operating them are capable of doing so at the lowest cost, while keeping acceptable service levels and following all safety procedures.
(Getting off soapbox-)