Knights of the Old Republic (KOTOR) and Mass Effect (ME) are Role playing game series at least started by Bioware. A discussion with HellJumper made me think about it randomly and I decided to pull this off the top of my head since I am currently bored at the moment.

The Main Character
-The Main character is fully customizable to the player
-After the First planet/mission you get a promoting, to Jedi in KOTOR and Spectre in ME (This only applies to the first games)
-Both characters are in a sense "repromoted" in the second games
-Both Main characters can be a soldier class (Only similar with KOTOR 1)
-The main characters can use powers of some sort
-The player can have romances with party members

The Party
-Carth and Kaidan have the same voice actor and both have something to do with piloting your ship
-Atton Rand is similar to Joker in that he is laid back and wise cracking and pilots the ship, although
-Something about Tali reminds me of Visas Marr
-Veetor survives the disappearance of human life on a planet, like Visas Marr, except her instance was far more serious
-It is possible to have a party member die at some point in the game on the player's choice

Your ship
-At the beginning of the second games the ship either gets damaged or is damaged, the Normandy is initially fine and later destroyed early on, and the Ebon Hawk is already damaged but later fixed.
-Both ships can be explored when the player wants to.

Weapons
-The gun weapons in KOTOR are similar to that in ME

Navigation
-You navigate with a galaxy map, though the one in ME is bigger

Locations
-The Citadel (ME) is similar to Citadel Station (KOTOR2)

I'll post some differences and maybe some more similarities later. I know there are probably more.

Bioware admitted to using KOTOR as a big (HUGE!) influence for Mass Effect so im not suprised at all.

It is expected.

Mass Effect is pretty much a 7th gen version of KOTOR.It's bigger,cooler and better

mass effect 2 still the best i never even heard of that game untill i saw it on youtube 2 months ago lol

Some of the missions in KOTOR are similar to Mass Effect 2 loyalty missions. Bastila loses her father(Tali loses her father), Carth has problems with his son(Thane has problems with his son). Also the name of the Collecter General in ME2 is the same as the Republic ship at the start of KOTOR2(Harbinger).

They should make a KOTOR 3.

Well they are both made by Bioware. So it should be expected.

KOTOR charatcers barely have any emotion.They sould have atleast have facial expression and better voice acting in KOTOR 2.The charatcer's are kinda like robot's.They just stand there,state there problem pretty plainly and expect you to feel sorry for them.

The charatcers in Mass Effect on the other hand actually sound like real people with real problems.Just look at Tali's loyalty mission.