At the time of launch in 2008, the Canon EOS 5D Mark II was a groundbreaking camera. Its predecessor, the EOS 5D, had already been very popular among professional photographers. The 5D had a 12.8 megapixel full-frame sensor and was much smaller, lighter and cheaper than other full-frame DSLRs at that time.
The EOS 5D Mark II wasn't just an incremental upgrade. It was a great leap forward for Canon and many photographers: a robust body of similar size as the original 5D, quite attractively priced, boasting a full-frame sensor with 21 megapixels and cutting-edge dynamic range and low-light performance. 21 megapixels and the image quality delivered by 5D Mk II may not seem impressive at all by today's standards, but that was 2008 and the standards were completely different.
It was also the first full-frame DSLR capable of recording Full HD video, and this feature was probably the main reason why this camera was so succesful. Suddenly, many photographers and videographers were able to record stunning films and achieve shallow a depth-of-field with their existing lens collections.
Canon phased out the EOS 5D Mark II in 2012, and at the time of writing, the current model in the 5D line is the Mark IV. Since the introduction in 2008, many other DSLRs and mirrorless cameras have surpassed the popular 5D II in terms of features and image quality. Nevertheless, this camera will remain one of the most influential and revolutionary DSLRs for a long time. Many owners, such as yours truly, will remember it well and continue to have sentiment for it.
I no longer own this camera, I sold it a few years ago. Below them some of the photos that I have taken with it: