This was okay. The idea of time travel always makes my head hurt... Plus, they have not really spent any time indicating that they were working on this new drive, and all of a sudden they are announced it was done.
There were flashbacks going back and forth between the past and present and in the end the present Kim and chakotay save the past Voyager.
I really liked the previous episode, so maybe watching them back to back hurt my opinion on this one...
They did a great job with makeup, making Kim and chakotay seem 15 years older.