What >>4207561 said, it's not bad and did some innovative things, like introducing saving stations, the spider ball and the current Varia suit design, but it really suffered from the systems limitations (or rather, being an early title, the inexperience of developers in working with those limitations).
Biggest drawbacks (in my opinion) are the way they utilized screen space, the repetitive gameplay and environments (M1 suffered from this too, but at least you could see the entire width/height of the room and they were in different colors) and the music. The tunnel main theme is great and I know some people go out of their way to defend the cacophonous rest of the soundtrack, but to me it's just really unappealing.