It's one of my favorite series and is a combination of RPG and TPS. The combat in the first game is pretty difficult at first, until you level up your skills (DO NOT try to snipe). The first time I played it, I actually quit in frustration and didn't try again until several weeks later. Vortex3D mentioned that you can't play ME1 like a shooter, because your guns overheat too quickly -- but later in the game (or new game+), you can upgrade your weapons so that they never overheat. As the series goes, the combat is refined at the expense of certain RPG elements (eg. you can't customize/upgrade weapons and armor to the same extent as ME1). ME2 is my favorite, but ME1 (despite its poor frame rate and clunky cover system) is special because it introduces you to the Mass Effect world. If you are a sci-fi buff, you will love this series (the storytelling is absolutely superb). It'd be awesome to play all 3 games consecutively for the first time, without even having to change the disc (I hope they go BD-50).
It will be interesting to see how the series continues, with both Bioware co-founders having retired recently.