Going by at least the ones I played:
KOTOR 2: Very decent followup to KOTOR. The story is good, but sometimes really straddles the line between being an interesting take on the Force and the Star Wars equivalent of le enlightened centrist. The ending portion was pretty damn rushed, which was a shame, since at least going by the restoration mods, it could have been pretty interesting.
Alpha Protocol: This one I definitely stand by. While the gameplay portion could have definitely used some refining (Stealth in particular), the story is solid and has quite a bit of replayability.
Fallout NV: The only decent Fallout that exists this side of the Bethesda acquisition. It definitely has flaws, but it stands head and shoulders above any other Fallout Bethesda made by a wide margin, especially considering the shitty game engine and the very short time frame.
Pillars of Eternity: I tried playing this one 2-3 times and dropped it out of sheer boredom every single time. The story would have been called generic even in the 90s, the characters were completely flat and the gameplay was nowhere near as good to carry the game.
Tyranny: Basically an improved version of PoE. While the game starts really well, it was rushed like hell, to the point you can almost feel the crunch around the second half onwards. The ending is so sudden I thought the game was bugged the first time I played.
Overall, they had some decent games back in the day, but as far as I am concerned, I am definitely not buying any more games just based on the "Developed by Obsidian" tag.