Ok, so I've had a chance to really play all of the different heists.
Diamond Heist is AWESOME. I haven't beat it yet, because it's also really damn hard (not to mention, "hard" is the minimum difficulty allowed to play it). It's the only map where you actually need to use stealth to be the most successful, and if a guard catches you, all hell breaks loose. You can supposedly pull off the entire heist without shooting anyone, but don't quote me on that.
Panic Room is closer to the First World Bank than anything else. It's the same idea at the beginning, like you're "hiding in plain sight". You're about to make a drug deal in an old run-down urban apartment building when then you stick up everyone and fend off the entire building from cops, covering multiple floors as well as the roof. You have to saw open the room in the middle to get the cash (or gold, can't remember). I haven't beaten this one either yet though.
Heat Street is much more linear and repetitive, both in a good way and bad way. It doesn't have as much substance as the other heists, and it throws a ton of enemies at you. It is kind of neat though, because it takes place outside, and you're running through a downtown city street trying to catch the van of a partner who betrayed you. I managed to beat this one last night; surprisingly so, because it's really goddamn hard.
Slaughterhouse is fun, also really damn difficult (like Diamond Heist, you aren't allowed to play it on any setting lower than "hard"). The beginning is pretty awesome, you lure in an armored van through a special back alleyway, and it suddenly gets plowed to shit by a bulldozer. The van goes down over a wall and lands in the roof of a slaughterhouse, where most of the action takes place. Seems kinda short, but I haven't beaten this one either, so maybe there's a twist or something in the story that I don't know about.
Green Bridge I've admittedly played only once, and didn't get far in, so I can't comment much on it. But it seems fairly close to Heat Street.
Awesome, awesome game.
I did create my own game, picked up three people. 2 of them had a hard time connecting, and while me and the other guy were playing it took them 5 minutes or so to eventually join. But we were having a decent game, and right at the end all I noticed I was the only human in the game! I recorded it so I'll have to look back and see if they were disconnected or just left. Its just really difficult to get a good game going, for one reason or another.
That sucks. I've had some pretty good luck in getting a solid team of people to play with me. Last night we had a really good group of people playing together, and we managed to finish playing Heat Street, which was quite a feat.