1) For one, Mass Effect 1 doesn't run like shit like it does on 360 and PS3. That's a big plus already.
2) You can easily get better than 30 FPS with 1080p if your PC is decent(mine have 8gb ram, quadcore AMD CPU 3.2 ghz and a 560ti, i get 60 FPS almost everywhere), you don't need the latest video card or CPU to run them this good. The games actually run better than fucking WoW, but the game has always been a mystery for me as to why i can't get constant 60 FPS. :lol
3) There is some fanmade mods that can give you higher res on characters, although i guess it might affect performance.
4) Aiming is much easier/faster with a mouse, but that's already a given with shooters on PC.
5) You got 8 shortcuts for powers without needing to use the Power Wheel. I don't think console versions get that much.
The only downside i guess is that they don't come with gamepad support, and that the mouse wheel doesn't even fucking work in ME2. Which sucks... having to click & hold a sidebar to scroll it down on a PC game? The fuck?
Also, no keyboard shortcuts for menus for ME2/ME3. Have to first go through the main menu to reach the powers menu, journal, options, etc.