The problem with Obsidian is that aren't a developer, they are scabs. They come in and use an existing engine to make a sequel by the numbers, typically in cases involving a publisher wanting to squeeze more out of a game developpedby a departing developer.
Aaaand you are completely wrong. As in completely wrong about everything except reusing their engine.
Yes, they used the same engine for KOTOR2. No, it was not at all by the numbers. They explored the star wars framework in a very interesting way (which was then completely ignored because it was COMPLETELY different in tone to every single other thing done with the star wars franchise). It's a shame their dev time got cut short. It is considerably closer to Planescape: Torment thematically than to even the previous title.
NeverWinter Nights 2, could ARGUABLY be said to be by the numbers, but even the original campaign is fairly unique, it does not take itself as seriously as many other games, it is fairly tongue in cheek in how it deals with D&D, which is a pretty good thing. Yes, the original campaign can feel fairly generic, but at the same time it is more or less a pretty light hearted take on the setting. Now, the expansions...
Mask of the Betrayer is ALL but cookie cutter or by the numbers. Once again, much closer to Torment than to any other title, both in theme and in execution. It is a serious title, with great writing. They used an improved version of the NWN engine, unfortunately it is rather poorly optimized, but damn if it doesn't try to explore the setting in pretty interesting ways.
Have not tried the third expansion, but I've read it was their attempt to make something similar to the Gold Box games. I have not tried those either, so I cannot comment on that.
Dungeon Siege 3, have not played. But they made the engine for that inhouse. Never played any of the DS games, though. Can't comment.
Alpha Protocol uses the Unreal Engine, but it does not use a variant used in another game. It is also unique in how it is structured. It is not flawless at all, but it is one of the most satisfying experiences, every single choice matters even if the destination is eventually the same in the end. It is the single most REACTIVE game I've played, and strangely, the most tense segments are the dialogs. God damn, it is a great game.
New Vegas? By the numbers? What?
It does use the F3 variant of bethesda's engine, but saying it is a by-the-numbers sequel is complete bullshit. It IS the proper fallout 3, or the remnants of it. It is by all means a labor of love and a true sequel to fallout 1 and 2, thematically and IN NARRATIVE. Hell, even the gameplay is considerably improved from 3. Better written, way better world building, and it ties in with the previous titles.
So yeah, calling them scabs or "wanting to squeeze more from a departing developer" is the single most wrong thing you could have said about Obsidian. If anything, they try to do things differently, explore different avenues, and focus more on writing and a very, very ambitious plan. Their ambition in their design is also why their titles end up being buggier or less polished.
Edit: Was I trolled and reacted to bait? Dunno.