These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
The N64 port. It has completely new levels and a different story, but the animation takes a noticeable hit and the crouching is removed.
The Playstation version averted this, although some features and a lot of levels are missing due to the limitations of the controller. But at the same time it had its fair share of unique content to make up for this (mainly visual effects such as lens flares, but in particular there are more Strogg types; the twin-railgun Arachnid and the giant 'Guardian', a foe physically bigger than Makron'sJorg Suit, which holds the Anti-Matter Bomb you need to destroy the Gravity Booster).
That One Boss: Ground Zero has the Widow Guardian and the Black Widow, Final Bosses, who can summon Stalkers to piss you off and shoot Plasma Beams everywhere. Oh, and if you attempt to use Invulnerability, Quad Damage and/or Double Damage, they automatically use an Invulnerability to reject all your attacks under until your powerup's effects run out.