My Favorite: (+) Pixel Junk Monsters & (+) Bionic Commando Rearmed. I got the most playtime and enjoyment out of those two.
My least favorite are: (-) 1942: Joint Strike & (-) Wolf of the Battlefield: Commando 3.
My other positive / negative PSN games that I've played the full versions
(+) Super Stardust HD
(+) Pain (for a short time)
(+) Penny Arcade Episode I & II
(+) Cuboid
(+) Flower
(+) Wipeout HD
(+) Magic Ball
(+) Calling All Cars (for a short time)
(+) Pixel Junk Eden
(+) Elefunk
(+) Flow
(+) Tekken 5 Dark Resurrection
(+) Linger in Shadows
(-) High Velocity Bowling
(-) Novastrike
(-) Rag Doll Kung Fu: Fists of Plastic
(-) Echochrome
(-) Savage Moon (maybe I should give this game another chance)
() Age of Booty (need to play more to properly judge it)
I've played a lot of PSN games and as you can see I've had lot of fun experiences. A lot of these games I don't play for more than a week, but for the small price I really enjoy the quick diversions between big retail games.
Also (+) Warhawk & (+) Burnout Paradise. I have the retail discs, but these games are on PSN as well.
Next on PSN I'm really looking forward to: Fat Princess & Trine this summer. Might get 1943 also.