The Mass Effect series is really good. It has many of the standard elements of an RPG of its type, but it avoids many of the flaws of its counterparts.
The first thing that has to be addressed for both Mass Effect games is their length. It's standard for games in this genre to be 80+ hours, with enough missions to occupy twice that length. Of course, a lot of that is walking overland, so that's not really content. In Mass Effect, you're either in a mission, or you're not. The closest thing to an overworld is the Capitol city space station, or whatever you want to call it. That place has plenty of missions to do, so there is never a place in the game where you're just trudging along, waiting until you get to the next city, or whatever.
Taking all that in mind, both Mass Effect games take about 20-25 hours, even if you do a lot of the optional quests. This is not necessarily a disadvantage though. People like to mock the idea of a hero tasked with saving the world wandering off and doing chores for losers. Although there are a few trivial missions available at the beginning of the game in the starting city, after that, any missions have lives at stake. This helps retain the idea that Shepherd is a real hero, who only does stuff that needs to be done.
Speaking of Shepherd, Mass Effect does a great job with character. The NPC's in Mass Effect 1 are pretty good, but Mass Effect 2's characters really shine. Even better than any of the NPC's is your own character. Shepherd is a one of the best starring characters in any games I've ever played, and it's largely because you get to choose who it is. You get to choose the appearance, (make sure to play without your helmet visible, the face is a big deal) and you get to choose the personality. Being able to import your character into Mass Effect 2 really helps, because it's hard to make a face that looks like what you want. The one thing I don't like about the advertising of Mass Effect is that they show us Shepherd's face. This would be fine for most games, "But that's not my Shepherd! Who's that impostor?"
The Renegade/Paragon dichotomy is infinitely better than the Good/Evil system of other games. I know Yahtzee has ridden this entire thing to the ground, so I'll be brief. In games with Good/Evil systems, Good and Evil are generally idiot options, with the Good options being stupidly moralistic and self-sacrificing, and the Evil options being cruel for its own sake, making you look like a jerk with none of the bonuses. In Mass Effect, "Paragon" isn't Stupid Good, it's "Relying on Principle", and tending to rely on people and the laws. Renegade isn't Stupid Evil, it's "cutthroat", or "Sick of all this being polite and ****". The best part is that the Paragon and the Renegade still have the same goal, Renegades feel like taking shortcuts along the way. This means you can realistically take a Renegade action even if you've been doing Paragon actions most of the time, and vice-versa. In other words, you don't feel constrained by your previous decisions, you feel free to be the character you want to be.
There are some minor complaints, no matter how much time you spend on designing someone's face in Mass Effect, they still end up looking like someone nicknamed "Fishface". In both games, there's an occasional pause between lines of dialogue, which can make the conversation stilted, especially when one person is supposed to be interrupting another*. The combat in ME1 is a little awkward, especially when compared to ME2, which has a hugely improved system. The dialogue system (which is still great) can have some really weird and counter-intuitive options sometimes**. Quick guide to dialogue: Go paragon, and you're basically a Jedi. You can give comically simple advice, and people will just follow it. You can tell criminals to reform, and they'll act as though they had never heard of the idea of going legit. It's not so much that you become really persuasive, as it is the people you're talking to become really gullible.
Despite all this, remember that I still think that Mass Effect 1 & 2 are really good.
*Despite this minor flaw, Mass Effect does a million times better job of constructing conversations in a way that seems like you're actually talking to someone, instead of just accessing someone's data files through an oral interface.
**There was this one time that I was talking with a reporter about the time I ***SPOILER ALERT*** let the Council die at the end of Mass Effect 1, and I wanted to say "It was more important that I save the whole Galaxy than saving the council, then all life in the Galaxy being exterminated, including the Council." That seems like a reasonable response to me. When I chose the PARAGON OPTION(!), Shepherd said "I felt that humanity needed to cut itself free of the Council's influences" or something to that effect. In other words, Shepherd said "I didn't like the government, so I let them all die." That is not the calculation I made, and it doesn't seem very Paragon-ish.