Build quality, hardware
It has the familiar blocky design that Lenovo is known for, and a rubber-y outer coating, which is a fingerprint magnet, but easy to clean. It's nowhere near as sturdy as the old T series, I think it can maybe survive an accidental drop. The battery sticks out a few centimeters at the back. The inside below the keyboard has a very cheap plastic feeling, I can bend it easily just by pushing it a little. It's very light, I don't think it weights more than ~0.8kg. The quality of the keyboard keys themselves are satisfying, they have a very nice feedback, and are large enough to hit comfortably, but they butchered the position of some buttons (delete, insert, end, see screenshot), which would come handy for power users. Overall, I use it rarely, I prefer using an external one, but the times I have to use it gets the job done very well. It also provides two levels of back lighting, and a numeric pad, both of which I never used. There are no led feedback for the lock buttons, but there is for things like sound muting, mic muting. The Fn key takes the place of the left control, but fortunately they kept the option of switching them in the BIOS.
Lenovo kept the clit button (trackpoint), but added the worst trackpad I have ever used. It's dubbed the "clickpad", and it's basically a single, large slab of plastic, with absolutely no buttons. You can press the whole clickpad in, which registers as a left-click or right-click, depending on where you clicked on it, and how many fingers you used. It's like a touch screen, with multitouch support, you can use motions like pinching to zoom/scroll, two finger clicks register as rightclicks and three finger clicks as middle clicks (yeah, really). This is probably the worst piece of the otherwise still great laptop.
Check your BIOS version before installing, because you can brick the whole laptop, as in, you actually have to send it back for repairs, because the motherboard goes bonkers. Your BIOS must be at least on 2.08, to avoid this. There is a feature that is supposed to speed up resuming from hibernation, which requires a special partition on the HDD, but if that partition is missing, the laptop freezes before POST, and there is absolutely nothing you can do to fix it, apart from sending it back to Lenovo. I heard you can also disable this feature in the BIOS and that will also avoid the problem, but I couldn't test it, mine was already above the required version. Same thing happens if you try to replace the HDD with a different one, for the same reasons.
Disregarding that, Linux support is okay. You can get everything working, but there is some tweaking involved. I was able to get the camera, clickpad, trackpoint, screen backlight, media keys working without any hassles. I had to fiddle around a bit with the fingerprint reader. It's made by Validity Sensors or something, and libfprint does not support it by default. I had to install a patched version to get it to work. There are a lot of tweaks out there for the clickpad, refining what click types the various areas register as, but I haven't really bothered with it, I use an external mouse (and some of them requires xorg.conf tweaking, which always results for me in hours of work with no return whatsoever).
For gaming, I'm running a bumblebee + bbswitch + primusrun setup, which allows me to keep the discrete card off, and only turn it on when there is something demanding it. I only play DotA2 (because what else do you need), the nVidia Quadro card provides a 60fps at relax time, but it drops down to 30-40fps when the action starts, at modest rendering settings and 1920x1080 resolution. It's not as fluid as it is on a desktop, there are some noticeable tearing when there is a lot of things going on, but it's perfect for getting my fix. The only problem is the heat. I have developed a very peculiar position of playing, which involves me sitting with my legs extended, laptop on my lap, right hand beside me on the external mouse (on the bed), and when the nVidia card spins up, this becomes a very effective birth control method. This thing heats up.
Battery life is excellent, at least for my standards. I'm used to getting 2:30, but I'm getting 5 hours out of this baby, and that is with the discrete card online. Disabling the discrete card also involves a bit of fiddling, bbswitch was reporting some kind of "argument mismatch" error when it tried to shut it down, but that was solved by appending acpi_osi="!Windows 2013" to my kernel parameters, for whatever reason I can't remember. I have to do some more testing to see how much it lasts with the discrete card shut down.
Oh yeah, get the intel wifi card, and not the realtek one. The driver for that is still very new, I have a friend who still has problems with it, even on 3.16. The intel one works out of the box.
Another thing that was a pain in the ass to track down, was the docking station. If you dock the laptop, and plug 2 external monitors in, they will always be mirrored. XRandr will report that there is 1 external monitor, absolutely oblivious to the second one, no matter what parameters you try to force it to extend. Turns out that this has to do with a technology called multi stream transport, that the docking station does, and this needs support on the OS side. There are a lot of suggestions on how to get this to work, all of them involving things like xorg.conf configurations, or launching a separate X server. Trust me, none of these work. I have tried getting this to work for a good 3-4 hours, and there is only one thing that works: David Airlie. He's a guy working at Red Hat, who made patches to the linux kernel that adds support for MST. I recompiled the kernel with the patches included, and I can confirm it works. The patch is already merged into the kernel in 3.17 (which came out about three weeks ago), so wait until your distro provides it for you if you don't want to compile (it takes about 35 minutes to compile the kernel on this laptop btw).
There are two things that are not working at all, and there is no solution currently:
The audio out (jack) socket does on the docking station, I read a very succinct advice "it will never work, use the socket on the laptop" somewhere (maybe it was ThinkWiki), and the integrated card reader reports some problems at boot, and refuses to work at all.
If I could change some things, I would give it the "ice cool" casing that ASUS uses, move the pgup/pgdwn keys back, and replace the clickpad. Overall, it's a good laptop, I'm happy with it. Take reviews with a grain of salt, because according to someone on Engadget, Lenovo has been removing the negative ones