Just curious before I hit the purchase button... Are all of the DLC for FO3 decent at least? I have been playing fallout NV's DLC and beat all 3 of them leaving me feel a little satisfied, however I am dying for new content and, alas, FO3 holds the key for new content via the DLCs. So could someone briefly rank each DLC and recommend some to start off with? I don't have enough points to purchase all of them :/

All, except Mothership Zeta.
Broken Steel is number one, as it adds more content to the original story and new enemies to beat. It also raises your level cap by 10.
Others are usual DLCs that have emphasis on a single aspect.

Point Lookout is an adventure DLC.
Operation: Anchorage is a combat DLC.
The Pitt is a story/morality DLC.
Mothership Zeta is... Well... It's something. Has lots of pointless combat, very odd story and barely any exploration.

Okay, so BS and PL are no doubt must-buys.

Curious though, how useful are the new items from OA, the Pitt, and MZ?

And also, why not get MZ? What if I don't care too much about the exploration or story? What are the positives to MZ? Because on the XBLA, 15,296 people have given MZ an average rating of 4.5 stars. Which is higher than the Pitt and OA...

You should know that operation anchorage is extremely linear and feels like a typical FPS. I hated it. It does however have some pretty overpowered items so if you like that sort of thing you may want to get it.

As asgard said, Operation: Anchorage rewards you with few but very powerful items, ranging from high power sniper Gauss Rifle to Chinese Stealth Armor that makes you invisible (like a permanent stealth boy)
The Pitt adds more usual weaponry, ranging from a makeshift "auto axe" which is a two-handed melee weapon, to a scoped assault rifle called Infiltrator (unique version is Perforator). The Pitt adds the most new equipment to the game and it also includes four new raider armors.
Mothership Zeta gives you almost exclusively energy weapons that work on alien ammo found on the Mothership. Silly looking guns you see in 50's science fiction flicks, I personally never use them.

After Broken Steel, I'd say Point Lookout is the best buy, it's fairly large, full of surprises and, assuming you don't spoil it with the wiki, lot's of replay value. The Pitt is a good story but after the first two plays, you realise it can be done very quickly without missing anything of significance.