Okay, here we go. (And I don't care if the recent TU/patch fixed some of these bugs/glitches, this is from my perspective when I played and beat the SP before that stuff.)
What I liked:
- BioWare FINALLY gave you the option of sprinting forever
- There is no more (or barely?) any textures loading in your face unlike ME1/2 due to the unreal engine
- The new and improved way of unlocking your powers has been mainstreamed
- Modding your weapons is fun
- The online MP co-op is pri fun
- The AI has been improved since ME2
- Less loading
- You can explore the Citadel again (Not as much as ME1 but still eons better than ME2...)
- The "insta-grab" feature
- Taking cover is easier/better
- The "sprint and melee" feature is cool
- Free MP DLC
What I didn't like:
- The ending
- EA (How they ruined/rushed BioWare IMO)
- Online pass
- Sometimes when you're talking/talking to someone, Shepard's/their mouths don't move and/or their heads don't move or their eyes don't move
- The frame rate drops sometimes
- How Shepard was obsessed with that boy
- The "I'm stuck in a dark forest" scenes
- Miranda's romance scene was lame
- No loyalty missions
- The first DLC pack is already on the disc/unlock code BS
- Less squad mates to choose from
- Reviving teammates in the MP is sometimes a ***** due to the 'A' button doing too much like in Gears 1/2...>.<
- EA's servers blow
- The MP servers will prolly be shut down by 2014
- The MP is glitchy (Even more than MW2 was at launch)
There's prolly more but that's all I can think of atm. Discuss.