It was bought just in time too, as NeXT Software (nee NeXT Computer) after selling off their hardware division, was already starting the process of selling off or disbanding their OS business in order to focus on WebObjects. If Apple had made an offer six months later, there wouldn't have been anything to buy.
Like Apple, NeXT was known for pioneering technologies that would have a tremendous impact on the computing world, while at the same time failing to capitalize on these technologies.
When the merger took place, SteveJobs took over as Interm CEO of Apple, or iCEO (haha, like iMac, get it?). Most of the Apple executives were replaced by their NeXT counterparts, leading many news journals to say the merger was like "NeXT getting paid to buy Apple."
I've always thought of NeXT (both the software and the hardware) as 'Macintosh, Mk.2'. It was Steve's chance to redo the Mac, without many of the technological, temporal, and financial limitations of the first one, while learning from some of the mistakes made. But not all; the first NeXT Cube had no color (it was 4-bit grayscale only), and no hard drive - it's only form of mass storage was a 256 MB Magneto-Optical disc drive. The NeXT Cube was deemed one of the top collectibles of the new millenium by USA Today.
Some NeXT Cube links:
The lack of color may have turned out to be a mistake in the market, but it was an intentional design decision. Color printing at the time was expensive, inadequate and inaccurate, and Steve wanted a WYSIWYG display, and deemed color not necessary for NeXT's target market. I don't know what they were thinking with the MO drive though.
OK, I've done some research and NeXT has a bit on what they were thinking. In short, floppy drives were too small to install the OS and applications from, and usable-capacity hard drives over 40MB were still too expensive. Hence the MO drive.