I just finished my third play-through of the entire Mass Effect trilogy. That's a lot of time to spend with a single universe, even with one as big as Mass Effect's is - after all, there's only so much you can pack into a largely-linear experience, especially one with a very definitive beginning and a very definitive end (shitstorm about the series' peculiarly homogenized triple-ending notwithstanding).
For someone not particularly fond of big 'sit down, let me tell you a story'-type games, there's a few things that brought me back to Mass Effect more than once:
I could skip (almost) everything
When the primary means of imparting information is vocal or otherwise time-consuming methods, you tread a very dangerous line - drag it out too much, and the player gets bored; rush through it, and they may miss critical bits. The series did a fairly good job at avoiding both extremes in every game. Being aware of the general lines (and how I wanted to play the game) meant I could skip through a large portion of the chit-chat, pausing at critical choice moments - either deliberately or the game forcing it - and then get back to the action.
The unfortunate side, though, is that the critical cutscenes and other 'forced-must-watch' are some of the more boring ones. I like to max out the difficulty, so I died a lot during intense battles; and seeing the same boss intro or hearing the same voice-over again and again had a natural tendency to grate on the nerves. See below for another example.
Combat varied from game to game
My favorite, overall, was ME1 - unlimited ammo, but overheating weapons. I was not fond of the HUD - it was easy to overlook how little damage you were doing and how many of your shots did not land at all. Add to that poor squadmate collision and navigation (oh, no, don't mind me, just step into my line of fire, please), and there's a pretty abrasive combination. ME2 made some changes, but not exactly great ones - ammo was now limited, moreso than necessary, and the 'heavy' weapons just didn't have much punch. The HUD was much improved, and dishing out damage was definitely more noticeable. And cover was better than 'let's push into that wall and hope I stick', though you did lose an explicit crouch.
ME3 is much better polished - you can run fairly well, with slightly more ammo (about time), a much snappier HUD...but moving in and out of cover is iffy, at best. Auto-aim also screws you over more than it helps, especially with zoomable weapons. Retreat is harder, as combat situations are far less open and movable - you can't really back off to regroup most times. And don't rely on your squad to help you of their own accord - order them around maybe three or four times for a single action, then maybe hope they actually do it. On the bright side, you don't have to halt the action and dig through a menu to give orders; just point and shout. And then promptly throw your controller through the screen.
Less 'inventory manager simulator', more 'badass space commander' ME1 was awful at this - many enemies dropped an equippable item of some sort, almost always inferior to your current gear, but unless you have eidetic memory of all the weapon model names, and can flash-sort them by number, you'll spend a lot of menu-hopping. Never mind missing an 'optimize' button - you're comparing that shit side-by-side for minutes at a time. Or skip it and hope for the best.
ME2 and ME3 are better - no more endless swapping out, but you can still pick some variations on your equipment, aesthetic and / or functional. You can't swap at any time, though - usually just at the beginning or midpoint of larger missions. Overall, a much better implementation, and a well-needed breakaway from ye olde standard RPGs and their inherent min-maxing.
Travel refined as the series wore on
In ME1, planetary exploration is neat, until you have to descend to the surface every. Damn. Time. Sure, you can skip about 90% of it and still get the core experience, but if you want to be well-outfitted...grab a sandwich or something. Moving between systems is great, though - point-and-go, minimal travel times. Read about the population, landforms...yeah, yeah, whatever, let's move on.
ME2 and ME3 forgo the detailed surface exploration (save for some side-missions and plot points), but add inter-planetary movement via another depletable resource: ship fuel. It's an even trade-off - I like the former, hate the latter. In all three, there are plenty of places to go and things to see, and the visuals are nice if you want to stare at something pretty for awhile.
So, what does it all mean?
Through all the above, the story is woven directly into the game - I can go around and read every console, listen to every log, talk to every person - if I want to. I'm not forced to stop while I'm spoon-fed the current situation, intel on the big-bad, and what my next task is (save for a few cases). I can take the game as quickly or slowly as I want, and each time come away with a pretty awesome experience. There's a lot to be said about epic stories, truly - the kind that draw you into a world and make you feel for its inhabitants, get you actively invested in the tasks at hand; but there's a necessary respect for the player outside the game, in that he or she needs to have knowledge of the investment, and the choice to dig deeper or resurface for air at any time.
I'll dig out an abridged version of my favorite saying: 'If I want to read, there are books; if I want to watch, there are movies.' And that's about it. Sinking hours upon hours into a game is fun when the bulk of that time is game - y'know, active involvement rather than sedentary consumption.
