(Most of this was written before I finished ME3, so if you want my overall thoughts after I finished it, they will be at the end since nearly everything I said before is still true)
So I haven't actually finished ME3 yet (I'm maybe around 25 hours in), but I wanted to write a review now so I could give my thoughts before I reach the ending, which I've heard very bad things about, but it thankfully hasn't been spoiled for me. Overall so far, this game is fantastic. A good story so far, with many returning characters, some of whom are squadmates. Combat seems to be about the same as ME2, so that's still great and entertaining. And the opening to this game... man, I'd say it's about as good as the opening to ME2. It's really great. And about returning characters, whether they're squadmates or cameos, they're all done pretty well from what I've seen. One thing I really like about being able to carry over saves from ME1 and ME2 is that previously established relationships with the characters still matter, and any characters that died in the past games won't appear, which helps make ME3 really feel like a continuation of the story. I'm assuming you've played ME1 and ME2, but if you haven't then SPOILER ALERT - for example Ashley died in my playthrough of ME1 so she's not around, and her death is also mentioned in both ME2 and ME3. I also lost Jack, Zaeed, and Mordin during the suicide mission in ME2, so they are also absent and maybe mentioned at times.Any romantic relationships are also carried over, too. The game also looks great. It might be a little dated by today's standards, but that doesn't mean it still doesn't look good. The graphics are good and it is overall very aesthetically pleasing. The environments are interesting and diverse. Weapon and armor customization is still available, which is a nice addition. The music is also great as always. I, along with many others, really love the song "Leaving Earth" that plays during the intro. It's one of my favorite Mass Effect songs.
However, as much as I love the game, there are a couple small problems I have with it. Probably the biggest one is that the dialogue feels slightly less interactive. I'm pretty sure that you have fewer dialogue choices in this game. Conversations sometimes progress without you choosing what to say when Shepard speaks. However, that's a minor gripe, and many other problems are so small that I can hardly even think of them.
The DLC I've played so far is pretty good. I've got it all, but I haven't completed all of it at this point. I've completed the Citadel DLC, which is great for many reasons and I'd highly recommend at least picking that one up. The Omega DLC is alright. You get to team up with Aria from ME2 for a fairly lengthy mission, which is cool. It's not as good as the Citadel DLC though, imo. The From Ashes DLC is cool too, adding a new squad member, (SPOILER FOR THE SQUAD MEMBER) who is a Prothean, which is pretty awesome.However, as cool as the squad member is, it really isn't too interesting to me for the most part. I also think a character this important should've been in the game to begin with. I haven't completed the Leviathan DLC yet, but what I've played is fairly interesting. Overall, I'd say Citadel is a must-have. Omega and From Ashes are pretty cool too, but Omega is my least favorite so far.
Overall, from what I've played at this moment, I'd say you should definitely pick it up. So far, it's a great end to a fantastic trilogy.
*EDIT AFTER FINISHING GAME*
So overall after finishing Mass Effect 3, just about everything I said before is still true. There were a few small bits of the Citadel DLC I hadn't played, but my thoughts on that are the same. The Leviathan DLC is cool too, and actually quite creepy at a couple points, but not totally essential imo. Citadel DLC is definitely the best and the one I would say is absolutely essential. The Extended Cut DLC is also essential, as it expands on the ending that was originally in the game, giving more closure and wrapping it up better. However, it is a little bit underwhelming, since it doesn't expand on as much as I would've liked, such as the fates of squad members. It is free though, so that's definitely a plus. The ending overall is pretty well done, as far as the last couple missions are concerned. However, I was a little bit underwhelmed by a few parts, specifically (SPOILERS) the whole thing about the Crucible and Catalyst. I dunno why, but the whole thing with having the Catalyst in the form of a little boy and stuff seemed kinda off to me. The overall story and everything behind them are fine, but that part just seemed strange. I would've much rather had it in a form similar to Vigil in ME1. Minor gripe, though. But overall, the game is a great ending to a great trilogy, Highly recommend all three. Definitely some of the best games I've ever played.