Getting the exact time to complete is easy. Go into the stats viewer. In the first block they list total deaths and deaths per hour. Divide total deaths by deaths per hour to get total play time.
I wound up with 5.5 hours of play.
Also, with regards to the mini-gun baddies, use the zoom function on the machine gun. The machine gun is completely stable in this mode and accurate (at full auto) over a large distance. With the machine gun it becomes relativly trivial to drop the mini-gunners even when there are four or more of them.
As to value for play? I pre-ordered for $17 and I felt that while it was a bit short, I really enjoyed the experience overall. SiN isn't the best shooter out there, but it is certainly the most enjoyable to come out recently.
With retail $50-$60 FPS titles clocking in at 10-20 hours on average, 5.5 hours of play isn't a terrible value at $34-$80 for the same amount of game. If you pre-ordered each episode (assuming $17 becomes the norm) your cost to play time ratio would actually be a bit better for SiN than a number of recent AAA titles. It works out even better assuming that you don't pay tax for your Steam games (I didn't have to) and do for your retail boxes.
I would have liked to see a _little_ more content for the $17 (the game was also a little too restrictively linear), but I think that the current pricing scheme is acceptable if the quality of content continues to improve and the length of play remains the same (or increases slightly).
Edit: Removed some redundant statements and fixed some typos.
This comment was edited on May 16, 13:32.