I highly recommend Call of Duty 4. It has a great single player with good story and requires you to actually push forward and risk getting your butt shot off instead of the typical formula of "enter area, kill everything, go to next area, kill everything, etc etc" that most shooters have. In many areas if you do not forcefully push forward, you will not advance in the game. The multiplayer is also really fun and keeps you playing with a system that allows you to unlock many different weapons and bonuses called "perks". It also has a rank levelling system(it's how you get new weapons and perks) and has Challenges, basically the same as Xbox Achievements.
I do not know much about UT3, but from what I heard it might as well be a remake of UT2k4. KotOR2, it's not bad if you enjoy Star Wars games, but you'll spend most of the game switching back and forth between being nigh invincible to being as impotent as a child with a glow stick. Smart career and power choices can help alleviate the latter part of the issue.
Crysis is a really good game. Not as good as CoD4, but good. They basically took FarCry, stuck it with steroids, and gave you an AI intelligent enough to kill you if you screw up. If you enjoyed FarCry, get Crysis. Just make sure your computer can run it. My laptop is a year old and can run it fine, but I didn't get to see all the pretty extras in the graphics. Still looks good on minimum settings though. IMO, don't get this game for the multiplayer. It's kind of retarded. It tries to rip off Battlefield 2, but does a poor job of it.
I can't recommend Mass Effect. I'm a shooter, but I do play some RPGs simply because I love good storylines and let's face it, shooters aren't usually known for mind blowing storylines. The reason I don't play more RPGs is because they all seem to have a hard-on for ridiculously restrictive combat systems that require more number crunching than actual combat. What I like about Mass Effect is that it takes the story and class elements of RPGs and combines them with the combat aspects of a shooter: can be fast paced while still tactical and a little bit of skill is involved. Now, while Mass Effect has a great storyline, it has one big glaring flaw that breaks it imo: it's too short and full of filler. The main storyline can be beaten in no time at all and in order to lengthen the game, the developer decided to throw in random side quests and pointless exploration. However, if you do decide to go for Mass Effect, I urge you to have biotics in your party as immobilizing your enemies while you kill them is pretty much all the friendly AI is good at(I recommend the cop and the mercenary, both aliens, forgot their names). They left their brains at home.
(I double post and don't even realize it. wtf... >.< )
Democracy: rule by the stupid