Since there are so many people pushing for you to play it and only one other saying you wouldn't like it I figured I'd add a bit more specifics about why I feel you won't like it. I will mention before hand, however, that I am bias as a huge fanboy of the series and may have some difficulty telling you not to play it. Despite its faults I still think its a good game but I also have to remember that not everyone likes it. My wife, for example, who had a lot of fun in the second one absolutely hated the third one. I want to say you should play it because I think EVERYONE should experience Mass Effect, I love it so much I can't not want to share it. That being said I still don't think you'd like it. It's complicated... lol.
I've been reading Ringworld and playing Halo CE lately so I started to think about the Mass Effect series for a bit. But thing is, I never played ME3. I did really like ME1 even if flawed, the sci-fi universe felt very compelling, the story was interesting despite being about saving the universe (was well disguised we could say), the characters were interesting, the planets, the exploration, etc.
The third game is even more about saving the universe since its during the reaper war. There are very few new characters, honestly, with the exception of Vega and DLC. You won't be meeting a dozen new squadmates with interesting back stories this time around. There is little time spent getting to know your squad since at this juncture it is assumed you already know them and have a connection. Which you probably do, in all honesty.
Still, many of the characters from the first two games are sidelined for the majority of the game. Generally speaking you'll get one quest that relates to the characters in the second game and thats it. Tali, Garrus, Liara and Kaidan/Ashley are the only ones who join up with you again, leaving all others to do their own thing. Liara is the only one, however, that is with you from the start of the game (though Garrus comes in early) while the others you have to wait till halfway through the game to get. If you cared nothing about the characters in the second game, however, this might not be a problem for you.
There is drastically little exploration. Granted ME2 didn't have exploration the same as the first game but at least in ME2 all the sidequests involved you going to a planet. So it still had some sense of exploration. You could scan a random planet, find a distress signal and go investigate. In ME3 all this is gone. There are still some N7 missions here and there and side missions (some are timed, btw) but you don't go around exploring space and discovering missions yourself. Leviathan DLC added some sense of exploration in this regard but for the most part it is gone.
In ME2 you scanned a planet, found a mission and did it. In ME3 you scan a planet, launch a probe and then boom, that was the mission. You get some little war asset codex talking about how your squad recovered such and such but you don't actually do it yourself, its a instant success story. Remember in the first game how you could find hidden minerals and a few old ships in space now and then that weren't actually gameplay quests but did recover something? Picture that only for practically everything.
You get to visit a few worlds, yes, but I feel it lacks compared to the first two games. In nearly every instance of you visiting a world it is strictly for the sake of killing reapers or cerberus and has something to do with the reaper war. There are no hub worlds where you can just visit to explore around a while. You visit the worlds during a specific mission and thats it. I know this isn't entirely different from ME2's formula but it did at least have a few hubs to explore to add more sense of exploration. Though I guess this is subjective.
Mass Effect 2... like a lot of sci-fi series these days, they felt the need to take a lot of influence from cheesy hollywood space operas, which I didn't really like. I thought the main story was pretty boring most of the time, except for what wasn't directly about the real main story, if you get what I mean.
I'm pretty sure I get what you mean. For me the side quests were the main entertainment for ME2 aswell. There were just so many things to do. ME3 lacks this, where no sidequest really feels like its outside the main story. Everything ties back to the reaper war. With the exception of fan-service DLC that is Citadel, of course. Depending on how you feel about the main story this may or may not be a negative. I'm sure some like the consistency of everything feeling like it contributes to the overall goal. I don't think they're wrong but I still preferred the variety the first two games shared. They had a lot of cool little stories within them that were completely independent from the main plot.
I do feel the story made a lot of stupid decisions simply for the sake of drama which may be linked to the hollywood crap you're talking about. Such as what they did to the geth, for example. Though a lot of this is subjective in nature so its hard to give a definitive answer. To me what they did to the geth completely changed their entire 'character' and contradicted everything they stood for just for the sake of adding some drama to the scene. Because ~DRAMA!~
I felt like there were a lot of aspects of the story that were made overly dramatic just for the sake of drama but, like I said, its pretty subjective.
Now, my real question, should I try ME3? Apparently the story is even cheesier (like with that kid thing) and the main story even more generic. Apparently there's even less dialogue choice, as if that was possible, and it feels to much like it probably wants to tap you on the back for saving the galaxy (something I could care less about since I don't like there) and telling you how much of a hero you are, because of you, the gamer.
The story is fairly cheesy with a lot of emphasis on SAVE THE EARTH so if thats a turn off for you then I don't think you're going to be impressed.
That being said you don't get too much tapping on the back for your success. Not saying that it isn't there but what is there is fairly reasonable given what you accomplished. If they didn't remark on anything you do it would be a bit strange given how important everything you do is to the victory against the reapers. I suppose it depends on what you consider 'tapping on the back'.
As for dialogue choice yes you get significantly less. I don't care what anyone says the dialogue options in ME3 are crippled compared to the first two games. Do you remember Zaeed from Mass Effect 2? The merc Cerberus hires, older gentleman with a scar over his eye? Or Kasumi, the thief? I'm not sure if your copy of the game had them because they were DLC. Anyway, just in case you didn't let me try to explain how dialogue worked with these characters outside their missions.
Click interact button. Hear them rattle on about something. That's it. There is no cinematic camera shot, no dialogue wheel, nothing. You just walk up to them and they say something. Zero interaction besides hitting a button once. In ME3 this principle has been applied to damn near every NPC in the game that has a 'side quest' (the ones that complete instantly by scanning a planet). That doesn't mean dialogue choice isn't there because you do have options for the more important NPC characters that tie in the to mission more heavily
Still the quest system and its corresponding dialogue system has been reduced to Shepard just eavesdropping on random people. You don't even formally accept the quest, you just walk by as they happen to be talking about their problem then you fly to the planet they mentioned, scan it and then walk back to them and hit the interact key to turn in the quest.
If you felt ME2 took away dialogue choice then you're /really/ going to think ME3 does, IMO.
Does the side quests save the game? Are the characters still interesting and are there interesting planets? Is there any place, planet, city or side quest that are reminescent of real old school sci-fi like ME1 did? Any grand sci-fi moment? Like you might have understood, I'm more a fan of laid-back sci-fi stuff that doesn't too much take tricks from nowadays popular filmakers (which I don't like at all). Is there something for me here? You know, I can still play ME2 and enjoy it, but not nearly as much as ME1, still, I think there's still something worth for me in the game.
I've went over a lot of this above but will reiterate my points.
The side quests are extremely lackluster compared to the first two games, imo. The first two games had side quests that, like you mentioned enjoying, didn't tie in to the main story and were their own little plot lines. Yes ME3 has side quests but they all feel so tied into the reaper war that they don't really have the same sense of being a side quest t hat the first two games did, if that makes sense.
There are no hub worlds and only Citadel is visitable and explorable. You do visit some alien homeworlds for like two missions but they don't give you the same sense of exploration, imo, that having a hub would gives. You're there to fight things and blow stuff up, not to explore. You can look out at the back drops and go "ooo, pretty, look at this place" but the magic is hindered, I feel, by the fact that you're killing people left and right. While in a hub world you can just walk around and immerse yourself with the citizens and get a feel for the place, as it were.
IMO the sci-fi immersion takes a seat back in ME3. You're not exploring and immersing yourself in this vast universe rich with lore. You're shooting and chucking grenades at it. Though like I said earlier the combat is a lot of fun and a huge improvement over the first two games. So if you want to sit back and have fun in a war-focused sci-fi setting then you might enjoy it. Still, based on what you said you didn't like about the games and what you did like, I still think you'd be disappointed. The game is pretty cheap now so I'd suggest you still try it out just incase you do like it. Though I do suspect you won't. I personally love the series enough to say that even if all signs point to you not liking it the game is worth trying out. I'm just that much of a fanboy.