As a subscriber to SW:TOR, I got to play the final chapter of KotFE yesterday (it gets released to everyone else tomorrow, 8/11).
Some people don't like how it ends, but I dug it. It's a very 'Star Wars' ending. It takes the easy way out on some things, but it also has some solid character transitions in terms of good guy/bad guy status, and things are set up nicely for the next expansion, KNIGHTS OF THE ETERNAL THRONE (which comes out later on this year).
If you're looking for something to scratch that KOTOR/KOTOR II itch, you really ought to play through the 16 part KotFE storyline. It you start with a fresh level 60 character, it really won't matter what character class or gender you choose. It doesn't really matter if you take through a character that you've leveled through the main story either, but KotFE is a tad more interesting if you take your Imperial Agent through it because there are some established relationships from that storyline that tweak some of the main character interactions in an interesting way.
As to time: you can probably bang through the entire KotFE story in 12 -15 hours. Don't rush it, though....the story itself is pretty good. Also, don't be concerned that it's an MMO; the KotFE story is definitely a single player game for the most part.