9 Years with the 5DII
Context: I am writing this in 2017 and I have been shooting with this camera for over 8 years (Update: 2018 - nine years now, still using it...). It is still going strong! THE SAME DIGITAL CAMERA FOR 9 YEARS! I used to shoot a few days a month, but for the past couple years I shoot almost every day, certainly every week.
This camera is one of the most important Canon SLRs of the digital era. Possibly the most important, because many people started shooting Canon BECAUSE of this camera. (Nowadays, Canon - like most Camera companies - is falling behind in the 'breakthrough technology' category: how can anyone keep up with the insane pace at which Sony is flooding the market with new technology at such low prices?!)
My only complaint: The autofocus system is lame and way to simplistic. All modern cameras have more advanced autofocus than this old thing. Even the EOS 3 film camera that came out a decade earlier had an autofocus system that had way more features than this one. So, not the best camera for sports, but great for portraits and landscapes.
Uses and durability: As well as shooting landscapes, portraits, and weddings, I use this camera for long exposures of the mountains in the frozen winter, and to film the hailstorms that blow through Calgary in the Spring. But the hardest use on this camera has probably been its use by various elementary kids during the kids workshops with James Davidson. Still, not a scratch.
Control layout and menu layout is excellent. The only thing I would change, and I'm not aware of any camera that has this feature - a third control dial full-time dedicated to ISO adjustment. That addition is the only control-layout feature I would add (the newer mark III has the next best thing to a dedicated wheel, discussed below).
My favourite thing about the 5DII - the battery. I could shoot a wedding on one battery but I usually show up with the vertical grip (discussed below) with two batteries so I NEVER HAVE TO WORRY ABOUT BATTERY LIFE. For anything shorter than a full-day wedding, one battery is plenty. In other words, you could go on a vacation with one battery and a charger, charge the battery each night and you would be fine. The great battery life also helps in cold weather where smaller batteries (pre-2017 Sony batteries) would die quicker.
Use the menu page called "My Menu" (it has a star symbol). Select "My Menu settings" and add all your most used items from the other menus. This "My Menu" is one of the best things about Canon cameras. ...2018 Update: Sony now has this "My Menu" (also shown with a star) on their latest cameras.
This camera is where it all began - the first SLR to break the 20-million-pixel barrier. On occasion, I have tested out crop-sensor cameras, and I would recommend the 5DII over any crop sensor camera of the same vintage... even over some newer crop-sensor cameras. I prefer this camera over the Nikon D3200 for example. The 7D was a good camera - with better autofocus - and for sport/races I would choose the 7D over the 5DII... for all other types of shoots, I prefer the full-frame sensor of the 5DII. (I haven't tested out the 7DII, it's probably awesome.) Overall, the image quality of the 5DII was breakthrough for the time and you can still get modern, professional results as long as you keep the ISO down, or use remote flashes. According to some, the much newer EOS R (released September 2018) produces excellent results on a perfectly exposed photo at ISO 6400, and produces a useable image at 12800. That far exceeds the capabilities of the 5DII, which is only decent up to ISO 3200 in my experience. At ISO 6400, you basically can only use the 5DII for black-and-white photography as the colour noise is terrible at that setting.
I highly recommend the Really Right Stuff L-plate - I'm using the one made for the 5DII with battery grip. The L plate is rock solid. The only downside is it gets really cold in sub-zero temperatures. ...Painfully cold in some temperatures. But I love how it makes the battery grip seem more solidly attached to the camera, and as a result I use the vertical grip much more often. Obviously the main advantage to an L plate is the ease of switching between vertical and landscape orientation when using a tripod. I always leave the L plate attached to the battery grip (as in the image below) because of how solid it makes the battery grip feel.
The other HIGHLY RECOMMENDED ACCESSORY is the (relatively new) Canon radio-frequency flash system with the radio trigger ST-E3-RT, I find it very reliable. Only limitation seems to be distance of the trigger signal. One time, photographing in Banker's Hall I noticed I could not put my flashes all the way down the end of the hall as it was too far for the signal. Within a typical studio or most wedding venues, the system is reliable. And practical: The flashes typically stay in the same mode I last used them in, so all i have to do is turn them on and off. And adjust the power at the transmitter on the camera.
(2018 Update: Yongnuo makes a less expensive version of the ST-E3-RT called YN-E3-RT. They also make a less expensive version of Canon's big radio-controlled flash, the 600EX-RT. The Yongnuo is a great flash for the price. Personaly, I find the smaller Canon 430EX III-RT radio flash lasts longer on a set of batteries and is more reliable, but the Yongnuo costs a lot less. You can fire both the Yongnuo flash and Canon RT flashes from the ST-E3-RT at the same time, so in other words the two systems work as one.)
5D II recommended? Yes, its a good full-frame camera for landscapes and studio work that you should be able to pick up used for not much money these days. I would not recommend it for action, sports, kids, wildlife/animals: most modern cameras have more frames-per-second and better autofocus systems and would be better suited. For example, 80D: crop sensor but faster fps and better autofocus. Also, Canon resolved all of the 5D II's shortcomings in 2012 and called it the 5D III (see my 5D III review). The more recent and more expensive 5D IV was released and it actually had better image quality than the 5D II… but as of October 2018 the 5D IV is still too expensive for what it is, and now there is a more affordable option for people with Canon lenses: the EOS R. Having said all that, the 5D II is a good camera for subjects that aren’t moving much, such as formal and casual portraits, as well as landscapes. Canon L series lenses really are awesome and, this camera, bought used, would be one of the less expensive ways to have a full frame camera to mount those L series lenses to.