Okay, going to give this a try without sounding like a bitter old Fallout fan.
Having played the DLCs myself several time I think I can give you a good impression, for your and my own convenience I will handle them all individually before making a conclusion.
Lets start with Operation: Anchorage.
O:A isn't as much as an expansion of Fallout 3 but more of a sub game with in with some skill checks/mini games.
It is basically a straight forward shooter during which you have to carry out a couple of missions.
There is a little interaction with the guys who ask you to enter the simulation and characters within the simulation itself, but in general you can't change much of anything, including the ending of the DLC.
The Pitt, I find this one better than O:A and in some ways its even better than the setting of Fallout 3 as the location looks more intriguing to visit than Washington.
There are more options of choice in this game but the problem is that they mostly lead to nothing, except who you support on the end of the game and who gets to survive.
It is no a complete straight forward shooter like O:A the whole time but there are such segments in the game like the abandoned steelyard and an optional underground as well as the ending of the game.
While there is an element of moral ambiguity in this DLC it never really lives up to its premise, that is really something more time and work should have been put in.
Last Broken Steel, this is a bit of a tricky beast to classify.
As you know Broken Steel changes the closed ending of Fallout 3, allowing you to continue afterwards and carry out a new number of main quests and side quests.
One of the problems with it, ignoring some of the technical problems that came with it, is the breaking of any form of balance.
As you may know, in a general RPG you can never become a master of all, if you try to become a jack of all trades you often end up with a form of punishment, lacking certain skills or simply not being real good at the ones you have.
For this purpose the player can build in a party in most RPGs in order to recruit the people with skills the player lacks or is not good in, each member complementing for the weaknesses of the other.
As many people who have played FO3 can tell you, a gamer who has knowledge of the various stat boosting elements in the game such as books and perks, can through careful use turn his or her character into an expert of all skills.
Basically this would mean that your character in real life would be a rocket scientists, neuro surgeon, athlete, diplomat, super thiefm acrobat, and engineer in one, taking away any of the randomness that is part of an RPG and ensures that no experience is ever the same.
The problem with the new cap system is that people who did not become full experts in the normal game can become so now, taking away the challenge of building a character that is somewhat good at all things in general, into a character that in the end is simply good at everything.
The new perks also disastrously unbalance the game, some consequences can no be completely eliminated like the permanent loss of the dog companion.
Even reputation building is undone, through one perk you character who is perhaps a drugs dealing, innocent people murdering, child enslaver can be turned into the most beloved man of the entire wasteland, eliminating the consequences of your deeds.
As for the main quests, well people who liked Fallout 3 will be glad to be able to continue, but to be honest; two of the main quests are yet again straight forward shooters with a few choice elements while the third is basically another errand boy quests like you may have encountered in Fallout 3 several times.
You do get to visit some new locations but outside the quests they are part of you most likely will not get back here once you have gathered everything of importance.
Some of the new weapons and armor introduced in the new DLCs are nice but some of them simply serve as upgrades to weapons in Fallout 3 and not as alternatives.
For example, you can get now a variety of Power Armors in the three games but with the exception of a few unique ones like Ashur which offer some stat bonuses, most of them are usually a better version of an earlier one.
The same goes for weapons, if you used laser rifles before you can now upgrade to the metal blaster and later to the tri laser which are simply laser rifles with more punch but not weapons with own unique properties.
The DLCs do add some more experiences to the normal Fallout 3 game but in my opinion do not change the gameplay that much.
What you do during Operation: Anchorage and The Pitt doesn't really affect the relations and situations you have in the Capital Wasteland.
If you free the slaves in The Pitt people will not suddenly mention this in any conversations or give you their support, nor will it make the slavers on the map more determined to get you killed at any cost.
The Outcasts will not like you even more to the point that they offer you actual membership or anything of that nature.
Broken Steel, well it add an epilogue and some little changes in the general environment but that is pretty much it.
In my honest opinion I can not recommend you to pay 10 dollars per DLC, despite the articles in which its mentioned that they last hours, that really isn't the case for a gamer with an experienced character, you will finish them in three hours or less.
I think you should wait until the DLCs become cheaper or unless someone offers the mission discs on Ebay for the acceptable price of 5 dollars if you really want to play them.
I hope this advice is of use to you.