i have never played a mass effect game so i thought since the trilogy was out nows a good time to start but i have a question what are the DLC the i need to buy for the 3 games that will give me the full effect of these games

From looking at a dlc list here is my take on "Story dlc" from the three games.

For ME1 the only one I think is worthwhile is Bring down the sky, but it doesn't have too much story impact introduces an alien race to the series.

For ME2 Lair of The Shadow Broker is the one of the best pieces, arguably the best dlc of the ME series for me. Lair of the Shadow Broker also sets up certain things in ME3. If the trilogy pack comes with Cerberus Network, you have Zaeed, but otherwise I think he is not particularly worth paying for (but he does have a role in ME3). I think Kasumi is really good dlc for ME2 (she also returns for ME3). For story purposes Arrival is basically required as its similar to a prequel for the start of ME3 (but the dlc itself doesn't set my world on fire). Overlord is a decent story, but non-essential for ME3.

ME3 you need From Ashes, Period. Leviathan is another one, for the story this is really important, but otherwise I would be ok passing on it. I didn't play Omega but Brad seemed to think its was mostly combat focused and not directly tied in storywise like Leviathan and From Ashes.

Feel free to ask me if you have any additional questions about the dlc.

@AlwaysBeClothing: thanks that is really helpful

I didn't think From Ashes was that great. I think Vinny completely overrates that character, probably because a lot of misconceptions about the fiction in general.

The only DLC I played in the entire trilogy is Shadow Broker, and it's great. The others aren't necessary for your enjoyment.

ME1: Bring Down the Sky. It's worth seeing to the end and has an amazing sky box if you're into that kind of thing. Play this before wrapping up the story.

ME2: Get the Zaeed and Kasumi packs if they're not included. It's a shame if you're playing the trilogy but aren't bringing in all the characters you can. Also, Kasumi's loyalty mission is well worth playing and also includes one of ME's most impressive vistas. Play this during the main part of ME2 when you're doing the loyalty stuff.

ME2: Overlord. It has a very dumb vehicles section but once you're back on foot it has some very cool twists on the visuals and I feel the end of Overlord is, perhaps, more impactful than Lair of the Shadow Broker's end. Play this whenever. I think it makes most sense during the main part of the game; well before the end.

ME2: Lair of the Shadow Broker. Overall, I think this is the most impressive piece of DLC produced to date; your milage may vary depending on how much you care about the core character. Play this either very late in ME2's story or after the story wraps up; it connects nicely with ME3.

ME2: Arrival. I don't think this is well put together, but it sets up the introduction of ME3. Play this after you've wrapped up the story line of ME2. For role playing purposes I'd even suggest to play this as the last piece of ME2 content.

ME3: From Ashes. Get this early to get the most out of this character. In the grand picture I don't think he is that interesting as a character but there are some fun chuckles here and there and he also brings a unique insight into Prothean culture. Play it early in the story line.

ME3: Leviathan. Very well put together for what it is, but I don't think it reaches the heights of Lair of the Shadow Broker. Play this at least before wrapping ME3's story line up.

ME3: Omega. Get this if you like Aria as a character or otherwise care about Omega as a location. Play it before wrapping up the story line.

I would say Overlord is better than decent, and if you're gonna be going from ME2 to 3, you might as well play The Arrival. It's not the best piece of DLC ever, but it bridges the stories between 2 and 3 so you don't just start ME3 going "what the hell is going on here?"

I can't speak to any of the ME3 DLC because I haven't played it, but I thought all of the ME2 stuff was worth playing, especially Lair of the Shadow Broker.

But yeah, just avoid Bring Down The Sky.

ME2 is a great game, you're in for a really engaging experience.

I am finishing up my last run of the first game. I had issues with the ally achievements. But I am powering though.

The first game still is framey as hell and the mako is still evil as hell.