There's always Ninja Gaiden Sigma! 9_9 6_6
Honestly, some of the best games you won't find deals on, because they're digital downloads. Then again, if you buy PS+ there's always the chance you'll get them, but that's a waiting game, and I prefer just having what I need at the ready when I want it. Games like Soldner-X: Himmelsturmmer, Soldner-X 2: Final Prototype, Super Stardust HD, the former 2 of which are excellent sidescroller shoot-em-ups, and the latter of which is a 360 degree top-down view astroid destruction/survival game. All 3 are mind-rapingly hard (hell, including my NGS recommendation, that makes all 4 of the games I've listed as patience-testing simulators, to some degree!) but very satisfying and also FUN titles. If you suck at them, they have difficulty levels, and they're just damn satisfying to play. Great soundtracks, sweet visuals, and they call back to an era of gaming that let you figure out what you were doing by just giving you the wheel and finding out on your own... and there's fireballs everywhere in the street. Have fun! =D
Personally, I supremely enjoyed GTAIV and GTAV, so I dunno what anyone's problem with either games might be. But if they're just not your thing, they're not your thing.
Other titles that kicked ass? LittleBIGPlanet was amazing (and very easy to underestimate, but if you stick with it for 3 hours, you'll find yourself losing sleep unable to tear yourself away before long), the Uncharted series is phenomenal (the 2nd is arguably the best in the entire series, but they all have their highs and lows) so grabbing one or all of those is a must, if you never played the original the Shadow of the Colossus HD rerelease is a spectacular title, and a great game to wrap up the list of titles that'll be keeping you busy for months to come is 3D Dot Game Heroes by FromSoftware (same developers behind the Souls series). So, in list format...
Disc:
Ninja Gaiden Sigma
LittleBIGPlanet
Uncharted 1, 2, and/or 3 (but definitely 2)
Shadow of the Colossus HD
3D Dot Game Heroes
Digital:
Soldner-X: Himmelsturmmer
Soldner-X2: Final Prototype
Super Stardust HD
In addition the Demon's Souls, that should round out your list quite nicely. Have fun! =D