Let me start out by saying that I've never wanted to like Glocks, and I still don't want to like them. With that said, I have gotten to spend a little time with a couple of G19s. One (a Gen2 or 3?) was a loaner while my other carry gun was getting some upgrades, and the other was one that I got to take the range a couple of times. Despite my desire to dislike them, I soon learned why it's such a popular model.
1) Take-down. It's easy. I'm what you might call "mechanically reclined," in that I don't really get along with fixing machines. I can field strip most basic firearms for cleaning, etc., but I'm not one to totally disassemble them. I know my limitations. With a G19, it's like "Field Stripping for Dummies." It comes apart into just a few modular parts, and goes back together very easily.
2) Lightweight. I like full-sized steel pistols. With a proper belt and holster, I don't find them difficult to CC. I cannot deny, however, that even a fully-loaded G19 is easy to carry. I carried the loaner for a few weeks, and could easily see carrying it all day, every day, with minimal fatigue.
3) Reliable. Let me also say up front that my sample size is statistically insignificant. I put about 150 rounds through a NIB Gen 4 G19. I got it, cleaned and lubed it (which was really easy, see #1, above), and headed to the range. Out of ~150 rounds, I had only one failure, and it was clearly ammo related. Specifically, I had some cheapo plinking ammo, and the bullet separated from the case on attempting to feed the second cartridge. Naturally, it didn't feed properly, and dumped all the powder into the gun and magazine. Cleared that bullet, blew into the gun to knock powder out, and moved on. Not a single other failure.
4) Accurate -- I'm not a fantastic shot. I'm competent, but I won't be winning the National Bullseye Championship any time soon. I was fortunate enough to have an honest-to-goodness firearms trainer standing by, giving me pointers (which I very gratefully accepted and followed). With all of those disclaimers, I have to say that the G19 put holes where I wanted them. It's probably more accurate than I am.
There are plenty of other excellent guns out there, but as little as I want to like Glocks, I have to admit that the G19 looks like a very good combination of weight, capacity, caliber, reliability and accuracy.