Tons of positive attributes, but for me personally the one thing that really sets it apart is the trigger. A true single action only/manual safety setup is rare, and even more rare when the rest of the attributes are included. Whether you like them heavy and crisp, or light and sweet, a 1911 trigger can do it and do it consistently.
Beyond the trigger, the ergonomics are awesome. Everyone may not agree, but many do. The safety is in the right place, the grip angle is "right", and if not, can be adjusted with mainspring housings and undercutting the triggerguard. Different trigger lengths are available to get the trigger finger in just the right place. Speaking of changing parts, there is the sheer variety available. From calibers to parts and accessories, they can truly be made to what an individual wants.
They are relatively simple. Most anyone can be taught to do most of the basic work on them or they can learn in on their own.
They are reliable. I understand there are stories of 1911's with issues or being unreliable, but a properly set up 1911 with good parts is very reliable. Unfortunately, there aren't many made today that truly have good parts, at least in my definition, throughout. However, it is typically the "little stuff" that can be replaced easily enough and without too much additional expense.
It's a classic. The history is undeniable. As mentioned above, next year marks 100 years after all.
Although some probably will, I won't say anything about .45 since you said 1911, and though they started in .45, "1911's" are now available in many different calibers.
I own and have owned a decent array of handguns and I am sure I will own some more in the future, but when it comes down to pure shooting fun with a handgun, I'd choose a 1911 or 1911 based design 9 times out of 10. They don't have to be for everyone, but I don't think they are going anywhere anytime soon...