One of the first things I like about Syphon Filter are of course, the controls. The game actually sets up the first stages to accommodate you to the control scheme and in comparison to MGS1, it's fast and fluid. You have a real 3D third-person environment instead of a mostly overhead isometric view of the action, which I believe gives the player greater immersion within the levels itself. Switching weapons, using gadgets, moving around, aiming, interacting with objects or switches, it's all intuitive, fast, and fluid, so it never frustrates you or takes you out the game. SF1 also has a surprisingly competent two-person co-op mode that people weren't expecting at the time.
Moving on to what may be the most controversial opinion, I believe Syphon Filter has a better, more grounded, and more coherent storyline. Metal Gear Solid 1 may not have been as bat shit as later games in the series, but it was still pretty nuts, and being nuts for the sake of being nuts can sometimes prevent you from writing scenarios that engage the player, instead you end up confusing them. Something like the enemy setting up a trap explosive within a train station destroying the entire tunnel, with you having to fight your way out of a blazing inferno, is a scenario that the type of writing MGS1 had wouldn't come up with. There are all kinds of twists and turns that engage the player throughout Syphon Filter, while in Metal Gear you just kind of shrug or maybe get a short laugh out of its cutscenes. Additionally, you have to face another issue with MGS1's storyline, and that issue would be it referencing two previous Metal Gear games that never released outside of Japan, as a result the context is lost on the player.
Gameplay is the most important factor for games, everyone knows this, and this is where I think the biggest difference rears its head. MGS1 has some decent gameplay, but it's very restricted, the controls take awhile to get used to, and are not very fluid or intuitive, and as you continue to play the game for hours the repetition and tedium starts to set in.
For Syphon Filter, the gameplay is fast, fluid, intuitive, and more open so you can approach situations several different ways, thus keeping things relatively fresh. The better controls play a key part here, especially for the gun play and overall movement, which felt so satisfying as you snuck or gun-run through well-designed 3D spaces. As you progress though the stages the game continues to present new ways to play, new enemies, new gadgets, and new combat strategies until near the end of the game. This makes it hard for repetition to start taking its toll on the player, and helps with replay value, something MGS1 has trouble with..
I generally believe Syphon Filter gave you the complete package, while Metal gear Solid was fine for it's time but it lacked the advantages Syphon Filter had, despite SF1 not having as high a budget or MGS' heavy marketing in commercials and gaming magazines. These advantages are what made Syphon Filter a surprise hit, and led to two more sequels on the PS1, along with Sony deciding to purchase Eidetic, the creators of the series. .
But over the years I must say that Metal Gear Solid has aged worse overtime, while Syphon Filter aside from some obviously outdated graphics compared to today, has aged much more gracefully, and I think the biggest part of that is due to it's fluid gameplay.
I may be in the minority here, but for people who have played both games how do you feel in regards to which of the two provided the better gaming package? Was it Syphon Filter 1 or Metal Gear Solid 1? Two big names in the stealth genres early days. (On consoles, I see you PC gamers, stay back!)