After spending an enjoyable day poking around in Portal 2, I feel the time has come for me to say some sensible things about this game.

First, and foremost: Valve has left most of the basic game intact, and once again there is a good amount of humor. Later levels have a more chaotic feel, and as such sometimes the puzzle itself is not always directly obvious.
Personally, I think it's a rather amusing game with a decent story. We're not talking great book level, but certainly better than some games I've played lately. Portal 2, like the original has some memorable amusing moments.
The biggest change gameplay wise are the gels and a new block. Red applied to a surface works as a super lubricant giving you a speed boost. The blue gel turns anything it covers into a trampoline.

As for the new block: it's a basically a mirror. If you've ever played prince of Persia SoT or a Zelda with the mirror shield, you know the kind of light redirection puzzles one can expect with this sort of tool.
Since this is in essence a first person logic/physics puzzle game, if you have trouble with those, this is not your cup of tea. Speed or reflex specific challenges are minimal. Timing on the other hand, can be very important: Think dropping onto platforms, or creating the required sequence of portals to guide an item.

Having said that, you can usually take your time or try again. There are no lives, so a death means loading the last (auto) save.

For a cross platform game, Portal 2 has a reasonably extensive options menu that can be navigated with keyboard, mouse or pad. A nice bonus is that having my x360 pad plugged in did NOT disable my other input devices like so many games do these days. That can be very annoying since often just unplugging your pad isn't enough. In these cases a game restart is required.

There are customizable key bindings for the keyboard. There was even a custom config option on the forums to get single machine split screen coop on pc. Although why this isn't included by default is beyond me. And for gamepads there are 4 button configurations. There is also a “normal” and “southpaw” stick setting.

There are settings for sound that include speaker configuration. Very handy to make sure it's running in 5.1, or to switch when plugging in that headset without leaving the game.

There are 2 levels of closed captions: subtitles only, and full. That last one seems to do a pretty good job. I could not find any omissions, however I cannot constantly read along fast enough.

Built in voice chat is also present, as well as some options to configure it.
Closer to the end, I had some trouble finding my way. There were times when I did not know which way I should be going, so trying to find the puzzle that needed solving got a bit tricky. There was no obvious marker, or other hint pointing me in the right direction. (That or I totally and utterly missed it.)
Looking all around using the zoom function usually let me find the right way.

One friendly tip: If you want a save for each level you'll need to do this by hand. I was halfway through chapter 6 when I wanted to check back something a few levels back. It was a bit of a nasty shock to find that there was only an auto-save for the current level. I could not even go back to the start of that chapter.
All in all, if you liked Portal I'd say this is worth getting.

At A Glance
Hearing:
Full captioning and subtitles. Valve did good job there, only reason I'm deducting
a point are the timers you hear when say pushing a button. They start ticking faster as they run out. That feeling isn't quite conveyed in the captions.

Visual:
Easy-to-read fonts. Colorblind friendly colors. Some trouble with visual ques.

Mobility:
Remappable keys. Multiple configurations. You need about 7 buttons including movement. As a test I played the game only with my 7 button mouse for a bit. You need forward/back, interact/jump, zoom, create portal, and alt portal. left/right can be left out, and use mouse look instead. If you can use an Xbox 360 pad on PC you're set as well.

Portal 2 has mouse sensitivity setting, including a windows override. You
can also turn mouse acceleration on/off, as well as set the amount.