Oldsmobile at the time (around 1990) had a reputation for being the car of the not-quite-well-to-do middle aged. Cars that were positioned upmarket like the Delta 98 and Cutlass Ciera were very cheaply and poorly built despite having standard features that were high end options on a Chevrolet or Pontiac or were exclusive to Oldsmobile and Buick.
Oldsmobile was one of the brands that decided not to participate in the 3.6L 60° V6 development program headed by Buick (that ultimately became the legendary Buick 3800 Series II), as Oldsmobile had been in an internal rivalry with Buick since the early 1970s and were instead championing their 2.3L inline four "Quad 4" which they showcased in the 1987 Aerotech concept that set a world speed record.
While Buick, Chevrolet, Pontiac, Cadillac, Opel/Vauxhall, and Holden all switched over to the Buick V6 as the default Oldsmobile stubbornly stuck it out with the Quad 4 and racked up a ton of development costs, eventually convincing GM upper management to put the Quad 4 in the volume selling Chevrolet Beretta and Cavalier and the Pontiac Grand Am to let economies of scale reduce the costs.
Oldsmobile, faced with an aging customer base and an engine that was costing them money, decided to break from GM's internal structures in 1990 and develop a flagship car that would knock down Buick from the second highest slot in GM's prestige hierarchy and allow them to ditch their entire lineup for something new. This first car would ultimately be the 1995 Oldsmobile Aurora, based on a concept from 1989 called the Tube Car, and which was the head project in development for the GM "G" platform. A platform which GM dictated that Buick also use for the upcoming eighth generation Buick Riviera, Buick's rival flagship car, in order to reduce costs. But Oldsmobile made a mistake in dictating that the Aurora have another unique engine, the 4.0L L47 V8. While it was based on the Cadillac Northstar V8 family, Oldsmobile modified it extensively -- fatally. The Northstar V8 in it's first few years was already fragile, and the L47 made those issues worse, damaging the reputation of the Aurora because of reliability issues.
By 1993 Oldsmobile was in full swing towards the reorientation however and was already focusing on their second car, the Oldsmobile Intrigue. The Intrigue was meant to reduce redundancy in the lineup by being the only mid-size car in Oldsmobile's stable, replacing three different cars. Oldsmobile's plans for yet another unique engineering project were interrupted however as it was mandated that the Intrigue use the same in-development second generation "W" platform as the Pontiac Grand Prix. Pontiac engineering essentially dictated the design of every W-body car of that generation, leaving Oldsmobile with little to do outside of styling.
Thus Oldsmobile turned to the Alero. The Alero was meant to be the volume seller, designed to compete in benchmarks with the BMW 3-series and and Lexus ES. By this time (1995) GM had begun heavily questioning the existence of Oldsmobile and heavily limited their autonomy on the development of the Alero. In a repeat of what happened with the Intrigue, ultimately by late 1995 Pontiac had taken the lead for the engineering of the second generation "N" platform vehicles, and the Alero (along with the Malibu and the quite literally rebadged Malibu sold as the Cutlass) ended up as a mechanical clone of the Grand Am, to the point where most parts are interchangeable. It was a foggy mirror of 1982 and the mistakes Roger Smith made of repeated and rampant badge engineering.
Oldsmobile spent the period from 1998 to 2000 marketing the Intrigue and Alero heavily, including the Intrigue Saturday Night Cruiser showcar, Alero OSV concept, The Alero California showcar based on the designs of then-current racing touring cars, and the Profile concept that was supposed to be a preview of the upcoming updates to Oldsmobile's design language. Ultimately this failed, and by December of 2000 GM had become fed up with eating the losses of Oldsmobile's engineering pet projects and announced they were shuttering the brand come March 1st of 2004.

I apologize that this is so long. There was so much internal dysfunction in GM between 1975 to 2008 and it affects everything so much that being concise is almost impossible even when talking about a single thing over a short period.