Munkeh -
Mass Effect is more of a what you want it to be - Shooter or RPG.
The story, customization, and statistics are VERY RPG-oriented. Great story, good customization based on stats, and your skill/level progression are very RPG-like (whereas a game like Bioshock has some things in it, but nowhere near what ME has).
The combat part is where your experience can greatly differ into an ARPG or a Shooter. The game allows for RPG and TPS elements. If you choose a soldier, you can run and gun, and use GRAW-like tactical methods to take down the opponents with very little turn-based, or otherwise "smart" combat.
On the other hand, if you rely more on Biotic and Technique powers to play your game (by picking a class that has those abilities). If you rely on them, you are forced to use your pause/turn based combat options MUCH more. Biotic and Technique users only start out with pistols (which aren't very good for TPS-style playing), so you would VERY rarely use them.
So it's what you want it to be, really. I've always used a mixture of both. Combat can get very shooter-ish and waste you, so there are points, if your smart, you absolutely have to utilize the game's "Magic" system effectively.
As for length, it can REALLY vary on how you play, and what you want to do. The main story arc (just playing the Story Planets, ignoring the small outerworld levels) takes roughly 15-25hrs, depending on your playing style. Having said that, the "staleness" of the game (as some have claimed) DOES NOT COME FROM THIS TYPE OF GAME PLAY. The main story arc is pretty much a 10/10 in terms of content. It's just phenominal.
The issues come from the side missions which you may, or may not, find repetitive. However, you do not "need" to do them unless you want achievements, level ups, skills, ect, but are not absolutely needed. The main gripe with the side mission planets is that many of them involve the same kinds of combat, and are mostly accomplished the same way (goto a planet, search all the stuff out, and kill the guys in the fortress). Most of these planets have cut and paste fortresses, with very similar layouts (the maps are very similar, but enemies, and actual inside content greatly differ). And the stories that take place on the side missions are, for the most part, very good IMO.
Doing the side-story missions take anywhere from 10-15hrs not including the DLC.
As for replayability, Mass Effect is one of the best RPGs I've played in awhile for replayability. It's quite a bit better than Oblivion, since Oblivion's claim to replay fame is the character customization (which ME has tons of), and the open-world aspect (which ME is more limited in this sense). However, the reason it's replayable is the dialogue. You have 2-5 various paths of choice to resolve a situation, based on your ethical and moral dilemma.
Here's an example of why the game's replayability is so great (and mind you, most missions are like this):
(semi-spoiler)
You arrive on a somewhat unfriendly Story World. To get to the next area, and find out what's going on in the level, you must obtain a Pass Card. To get this Pass Card, you must talk to Guy A, and eventually meet up with Guy B.
However, there are 5 different ways you can get this Pass Card, not just including Guy A:
1) Inform Guy A of corrupt activites on the planet, getting him to give you his Pass Card, negating story arcs from #2-5
2) Talk to Guy B, and do what he wants, and complete it "the standard way"
3) Do #2, but a Guy C "pops up" that you didn't talk to enough, or at all. Find out they want Guy A killed. They kill Guy A, and you mop up Guy A's Pass Card when he's dead.
4) Inform Guy A of plot #3, Guy A kills Guy C, and gives you his Pass Card as thank you.
5) Inform Guy C of Plot #3, but inform Guy C of the plot too - ending in a vicious gun battle, killing everyone. Loot dead bodies and get all their pass cards, and cash.
That's 1 story. There are many, many of those in the game. I tried to neuter the stories, but it's a brilliant story that takes anywhere from 3 minutes (my first choice) to well over 30 minutes, depending on the choices you take.
So replayability, to make different, game-effecting choices is pretty great. Not only this, achievements "carry over" to new characters: If you unlock the "Kill 150 enemies with your Assault Rifle", should you create a non-Assault Rifle using class, you can select that character to start with the ability to using Assault Rifles (same goes for unlocked Biotic/Tech achievements). So you can REALLY get some great classes by replaying over and over. My next character build, if I ever did a 3rd new player, would be a biotic w/ an Assault Rifle, which would just be about the deadliest combo the game could have.
