to pre-answer the same few questions:
definitely worth getting at 50%+ discounts:
sleeping dogs (dlcs are meh)
fallout, fallout NV
batman (both are really AWESOME and "rich" of batman stuff)
bioshock (all)
walking dead
dark souls
civ5
tropico 4
dear esther
to the moon
saints row 3 (get the full package)
gta full bundle (will come around)
bastion
portal 2
trine/trine2
kerbal space program
tomb raider reboot
all assassins creed except 3
mortal kombat (2 hour story movie, more for longtime MK fans)
dishonored
dead space
far cry blood dragon
just cause 2 (crazy gta style game set on corrupt tropical island)
deus ex HR (cool cyberpunk/scifi story, long time DX fans may not like it)
more borderline:
skyrim (need PC version and legendary edition to be good, need lots of mods to be better than average)
borderlands 2 (boring single player, need friends to play co-op)
defiance (shitty but cheap mmo, no sub)
assassins creed 3 (shitty story compared to rest)
deadpool (8 year old humor you may love or hate, game gets boring fast)
dead island
crysis 3 (like 8 hours of gameplay)
darksiders 2 (decent story but highly repetitive gameplay)
hitman (decent but short, really fun if you force yourself to be super stealthy but isnt required and not as stealthy as previous hitmans for last few levels)
far cry 3 (yeah the dlc is way more fun than the base, and doesnt require fc3 so weird)
max payne 3 (unless you really love cutscenes, which this game is 80%)