sozoluk

I like the 2 nighters cause it gives you a feel for that type of ship and whether or not
you think you would like to sail on it for a longer time - its not enough time to see
the whole thing or do everything but it is a great experience

As a general rule, the longer the cruise, the more cost-effective on a per-night basis it's going to be. The really short cruises are ridiculously expensive for what you get, IMO. Depending upon where you live, a 2-nighter could be a fun way to spend a couple of days but if the logistics of getting to the ship outweigh the [very short] fun of the cruise then I would say no.
 
Let's just say, I wouldn't do it !

The two nighters are fun if you can do it as a B2B. We did this on Disney to create a 9 day cruise, plus it gave us a chance to sail with family who could only do 2 nights. You're right, though about pricing. Our 2 night was half the cost of the 7 nighter, so much more on a per day basis.

Thought about doing one, but after really thinking about it, I don't think its worth it.
 
Just enough time to start figuring out what you like, knowing your away around the ship, etc. and then your in line to go home.
 
Plus the prices don't seem all that cheap by the time you had in the port fees & taxes that don't seem to be significantly lower than a 7 nighter.

Get on as early as possible and keep checking the cruise planner daily to reserve any must dos onboard.

A 2-night cruise is better than no cruise at all but it's over before you know it and it's a tease.  You will find you barely have time for anything (like sleep) so to answer your question, it's not enough time to see it all by any means but then again, it's still a cruise!