1. Are You a God? - Defeat the single player campaign on Professional. If you don't want to devote a whole play-thru on the hardest difficulty I can confirm that you can earn this achvmnt by just defeating each boss on professional. I found a thread on this on x360a suggesting you complete the first and last checkpoint of each level so that's what I did to unlock it last night. However, I'm willing to bet that it'll work with just beating the boss at the end of each level. Plus, after defeating the boss it goes right into the first checkpoint of the next level anyway.
2. Spores, Mold & Fungus - Collecting all the Artifacts. The achvmnt guide on x360a recommended going on to the next checkpoint for it to save but I can confirm that you do not need to complete the checkpoint. Simply follow the guide here http://www.xbox360achievements.org/forum/showthread.php?t=153637 load whichever checkpoint you need, find the artifact then you can quit to the main menu and load the next checkpoint and the artifacts will be saved. This is particularly useful if you miss some during your initial run-through like I did. This also works with The Ghostbusters Drinking Game achvmnt. The guide says you have to finish the last boss battle for it to pop but I was able to do it by the same means as finding all the artifacts.
3. The Destructor - Tally a property damage claim of $3,000,000. You don't need to have all 3 million before you complete the story mode. You can load up previous missions and tear the hell outta em. I recommend the Museum level, you can rack close to 1.5 million on this level alone. I found when entering the Civil War exhibit you can completely trash the room then proceed to leave and the door locks on you and all hell breaks loose. You have to wrangle up all the ghosts and the exhibit is magically rebuilt and ready to be trashed again. As for the opposite achvmnt titled Nice Shootin Tex!, where you have to finish with less than $100,000, you'll need to start a whole 'nother game and I recommend going through on casual, avoid using the Boson darts unless truly needed cause they tend to cause the most damage and try hard to avoid blowing up cars or trucks when on the Time Square missions.
Edit: Boss Battles: Azetlor The Collector, Library Mission: I personally found him to be the hardest of all the bosses. I actually had more trouble beating him on experienced than when I beat him on professional. My only real tip is to use the portals. After you rip his mask off he goes ape-shit. Stick close to one of the portals in the corner. He'll concentrate on Ray & Egon until they're down then he'll come for you. Just shoot his eye with the proton beam & boson darts till he gets close then jump through the portal and you'll be on the opposite side of the room, turn around and commence firing. It also helps to revive your teammates, giving you more time to shoot him until he knocks em down again.
The only other boss that gave me any trouble of professional was The Chairman: Lost Island Mission. You'll find his only move to knock you out is when he comes up the side of the platform after you take care of his minions, he'll warm up and then spin around shooting out a wave of energy that'll knock you and your teammates out. Just stick close to the big post in the middle of the platform and hide behind it when he starts warming up. He can't hit you here, but most likely will knockout all the other guys, so you'll need to revive them.
Hope these tips are helpful. Feel free to post any other tips you guys find, especially in regards to the multiplayer. I read that a few of the multiplayer ahvmnts are glitched and not popping for people. I also recommend that Meta add this to his list of waffles. With as few as 2 play-thrus you can rack up 890 points for the single player. The remaining 110 being for the multiplayer. The only real time consumer that I see is the Overachiever multiplayer achvmnt where you have to rack up 2.5 million bucks and 30 post game awards etc..