I agree with you on Conviction. I'm not sold on its gameplay at all compared to SC and CT. I'll give it a shot but I'm not as excited about it as I once was.
You can say that MGS isn't a "stealth" game, except that the series INTRODUCED the genre back with Metal Gear. Everyone expects the game to involve stealth elements and the transition to TPS-style play caused someone at Kojima productions to ease back the difficulty.
As for difficulty settings, I played on Solid Normal, the second highest difficulty for the initial playthrough. It's where I set all my games because I expect the game to offer SOME challenge at that difficulty. Mass Effect 2 did, BioShock did (other than the VitaChambers), most games do... unfortunately, MGS4 only hung me up at one point and that was the deck of the freighter... which I blitzed through like I would Gears of War. I shouldn't have to crank the difficulty to an obscenely high level just to get something out of the game.
You're right about R6... the older games were impossible to play without stealth and I'd like to see the series return to that a bit. Still, as is, the new games promotes stealth on medium/medium-high difficulties more than MGS4. I just played through Vegas a few weeks ago and found the game moderately difficult.
I don't think it's stupid to compare the MGS and SC games directly if you're comparing gameplay elements and nothing more. In that regard, the two series are somewhat similar, reside within the same genre, and after all, MGS4 kind of ripped SC's control scheme.
PS. BioShock wasn't a failure because of the VitaChambers but jesus, the game would have been SO MUCH BETTER without them. Increase save points if you need to but I hate games that give the player a get out of jail free card. It removes almost all the tension from the situation, which would have made Rapture even more creepy and intimidating.
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